Drupal 8.x

I am trying to install the module php mailer and smtp. Smtp installed fine but php mailer is showing some error while enabling. Can anyone help me out ?

This is the eroor that i am getting.

Please install the PHPMailer library by executing 'composer update' in your site's root directory. (Currently using PHPMailer library version Missing)

Since the upgrade to 8.5.1 (using composer and drush @sites updb) the user/login, user/logout & user/register are all displaying as 404 pages. 

Here's a stack exchange about the same problem https://drupal.stackexchange.com/questions/258805/how-to-debug-404-on-user-login-user-register-user-logout that I am not alone in having, there seems to be more than 5 others that have the same issue.

I have always manually updated my drupal 7 site, but recently moved it to Drupal 8.4.  Now I need to update it to 8.5.1 for the new security fix.  I am trying to do that following the recommended procedure using composer and drush but have not succeeded.

Using Version 8.4.5 -> upgraded direct to 8.5.1 caused website to display that it was having an error and would not load.

PHP errors logs: 

InvalidArgumentException: Field is unknown. in Drupal\Core\Entity\ContentEntityBase->getTranslatedField() (line 580 of /var/www/html/core/lib/Drupal/Core/Entity/ContentEntityBase.php).

Just got SSH access setup for Putty to shared Host server.
Connects and seems to work fine.
cd to core folder where composer.json was
Originally wanted to install ( on existing working Drupal 8 site ) advanced_help
that said required composer to install:
composer require 'drupal/advanced_help:1.x-dev'

came back with
Loading . . .
Updating . . .
Killed

Checked and saw NOT installed.

Tried test command:
composer update

same. . .

April 26, 2018 Frontend Performance in Drupal 8 in-house workshop taught at Isovera. This course is designed for Drupal 8 (or soon-to-be D8) developers and digital designers with a basic understanding of Drupal 8. 

The workshop covers new features in Drupal 8, performance configuration settings, a performance strategy (and performance budget), and techniques for front-end design and coding that can yield significant speed improvements across the board.