Warnings during Core Update via Drush

During Core update to from version 8.6.7 to version 8.6.8 using Drush I encountered several warnings I am unfamiliar with...

If I could get some help interpreting and which I need to address (and how/where), I would appreciate it.

Further I suppose since these warnings etc. That I have not seen during previous Core updates, I am wondering if this is something new in core that I must address, or worse if my distribution(s) need attention.

Since I am unaware if context is of importance, I will paste the entire session (including the repeated warnings) in case that will help.

Sorry in advance for the duplications, but that is what was generated during the session from "drush up drupal" to the end.

MY-ACCOUNT [~/public_html]# drush up drupal
Error while trying to find the common path for enabled extensions of [error]
project schema_metatag. Extensions are: schema_article,
schema_article_example, schema_audit, schema_book, schema_event,
schema_image_object, schema_item_list, schema_job_posting,
schema_metatag, schema_movie, schema_organization, schema_person,
schema_product, schema_program_membership, schema_recipe,
schema_review, schema_service, schema_video_object, schema_votingapi,
schema_web_page, schema_web_site, schema_course.
Update information last refreshed: Wed, 02/06/2019 - 17:56
 Name    Installed Version  Proposed version  Message
 Drupal  8.6.7              8.6.8             Update available


Code updates will be made to drupal core.
WARNING:  Updating core will discard any modifications made to Drupal core files, most noteworthy among these are .htaccess and robots.txt.  If you have made any modifications to these files, please back them up before updating so that you can re-create your modifications in the updated version of the file.
Note: Updating core can potentially break your site. It is NOT recommended to update production sites without prior testing.

Do you really want to continue? (y/n): y
Project drupal was updated successfully. Installed version is now 8.6.8.
Backups were saved into the directory                                [ok]
/home/indust10/drush-backups/indust10_mag_live/20190207015625/drupal.
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
The following theme is missing from the file system:                 [warning]
bootstrap.inc:276
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Creating default object from empty value ModuleHandler.php:236       [warning]
Creating default object from empty value ModuleHandler.php:236       [warning]
No database updates required                                         [success]
MY-ACCOUNT [~/public_html]# composer update drupal/core --with-dependencies
Package "drupal/core" listed for update is not installed. Ignoring.
Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Installing symfony/css-selector (v3.4.15)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing behat/mink (dev-master d5ee350)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing symfony/dom-crawler (v3.4.15)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing symfony/browser-kit (v3.4.15)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing fabpot/goutte (v3.2.3)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing behat/mink-browserkit-driver (1.3.3)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing behat/mink-goutte-driver (v1.2.1)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing instaclick/php-webdriver (1.4.5)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing behat/mink-selenium2-driver (dev-master 8684ee4)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing squizlabs/php_codesniffer (2.8.1)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing drupal/coder (8.2.12)
    Cloning 984c54a7b1e8f27ff1c32348df69712afd86b17f

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing jcalderonzumba/gastonjs (v1.0.2)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing jcalderonzumba/mink-phantomjs-driver (v0.3.2)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing mikey179/vfsstream (v1.6.5)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/version (1.0.6)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/global-state (1.1.1)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/recursion-context (1.0.5)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/exporter (1.2.2)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/environment (1.3.8)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/diff (1.4.3)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing sebastian/comparator (1.2.4)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/php-text-template (1.2.1)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing doctrine/instantiator (1.0.5)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/phpunit-mock-objects (2.3.8)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/php-timer (1.0.9)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/php-file-iterator (1.4.5)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/php-token-stream (1.4.12)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/php-code-coverage (2.2.4)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpdocumentor/reflection-docblock (2.0.4)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpspec/prophecy (v1.7.0)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing phpunit/phpunit (4.8.36)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing symfony/phpunit-bridge (v3.4.15)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Installing ircmaxell/password-compat (v1.0.4)
    Loading from cache

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
behat/mink suggests installing behat/mink-zombie-driver (fast and JS-enabled headless driver for any app (requires node.js))
behat/mink suggests installing dmore/chrome-mink-driver (fast and JS-enabled driver for any app (requires chromium or google chrome))
sebastian/global-state suggests installing ext-uopz (*)
phpunit/php-code-coverage suggests installing ext-xdebug (>=2.2.1)
phpdocumentor/reflection-docblock suggests installing dflydev/markdown (~1.0)
phpdocumentor/reflection-docblock suggests installing erusev/parsedown (~1.0)
phpunit/phpunit suggests installing phpunit/php-invoker (~1.1)
Writing lock file
Generating autoload files
> Drupal\Core\Composer\Composer::preAutoloadDump
> Drupal\Core\Composer\Composer::ensureHtaccess
MY-ACCOUNT [~/public_html]# drush updb
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
The following theme is missing from the file system:                 [warning]
bootstrap.inc:276
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Creating default object from empty value ModuleHandler.php:236       [warning]
Creating default object from empty value ModuleHandler.php:236       [warning]
No database updates required                                         [success]
MY-ACCOUNT [~/public_html]# drush sset system.maintenance_mode 0
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
Class Drupal\Core\Extension\Extension has no unserializer            [warning]
DatabaseBackend.php:167
The following theme is missing from the file system:                 [warning]
bootstrap.inc:276
MY-ACCOUNT [~/public_html]# drush cr
Cache rebuild complete.                                              [ok]
MY-ACCOUNT [~/public_html]#

I have verified the site and do not see any issues, so hopefully someone can put my mind at ease... or not!

Thanks