Error on CRON run : linkgenerator

yes it's the Drush output, and is version is :

Drush version                   :  8.1.16
Drupal version                  :  8.6.1

Do the incomplete block migration could be one cause ?

This error happen at the same time.Perhaps related ?
EDIT: I can reproduce the error happening when I run d6_term_node:1 migration with drush.Rollback doesn't clear the error on Cron.

Actually the Coffee bug doesn't happen so it's not really related.
This is the cron debug mode: https://gist.github.com/webmasterpf/3ec7da7b7a54ecb9c57eaa79d79faf9a

I need Drush 8 because I manage D6 and D8 websites until the end of migrations (8 websites to go).

Content of 2 differents content type cause this error and break the CRON.
No common fields, each use linkfield, reference entity field (taxonomy),image field(multi-value).
How can I do debug as #3 suggest ?

After looking into data in db and compare between D6 and D8, I see empty db fields for these linkfield.
I have a linkfield with no migration issue, and source db field isn't empty.
On my 2 content types with errors, there are db field:
For example, the field_lien_externe_url db field take normally url's OR NULL if no data, but it happens db field empty.
I think this could be the origin of the error.
So how can I replace empty data by NULL mention in db field ? search and replace in db ? To test my theory.

I compared records in content_field_lien_externe D6 table and node__field_lien_externe D8 table .
It appears that all records with NULL or empty label/field aren't migrated (ignored).
So the D6 table with 312 records go to 23 records after migration into D8 db. This is why the linkgenerator error happen I guess.

Can I force migration of all records with a custom migration module ? If yes, how to map them ? Actually I do this whithout changes on this error:

 field_lien_externe:
     plugin: d6_cck_link
     source: field_lien_externe

Reviewing records from working content migration, it appear that empty and NULL label are skipped as a normal way.
So my issue, come from a corrupted data or something like in a record...will not be easy to find.
EDIT: finally, records from the content_field_lien_externe table (D6) (199 non empty records over 312 in all) are dispatched in node_revision__field_lien_externe table (199 records) and node__field_lien_externe table (D8)(23 records). Are these 23 twice records cause error ?

I investigate more and more and I get the culprit node (one of) among all nodes for a content type that break CRON.
In DB records, I see a difference,perhaps the cause, but I don't know what about is it.This is extraction records from D8 DB:

bundle;deleted;entity_id;revision_id;langcode;delta;field_lien_interne_uri;field_lien_interne_title;field_lien_interne_options
page_fiche_formation;0;7;7;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;10;504;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;11;11;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;13;384;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;14;172;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;15;515;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;16;348;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;17;571;fr;0;internal:/node/270;Coût de la scolarité en initial Hors contrat;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;18;570;fr;0;internal:/node/270;Coût de la scolarité en initial Hors contrat;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;32;32;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;33;33;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";a:0:{}}"
page_fiche_formation;0;219;247;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";<strong>s:6:""</strong>a:0:{}"";}"
page_fiche_formation;0;262;476;fr;0;internal:/node/270;Coût de la scolarité en initial Hors contrat;"a:1:{s:10:""attributes"";a:0:{}}"

Difference is in the field_lien_interne_options field table.
page_fiche_formation;0;219;247;fr;0;internal:/node/21;Coût de la scolarité;"a:1:{s:10:""attributes"";s:6:""a:0:{}"";}"
Is someone know what kind of option is it ? Could it be the error origin ?

I test on another content type and I notice that records that contains "a:1:{s:10:""attributes"";s:32:""a:1:{s:6:""target"";s:6:""_blank"";}"";}" in the field_lien_internet_rp_options break CRON with linkgenerator error and content give a WSOD ( node__field_lien_internet_rp db table)
I edit this content and re-save it, and error disappear + CRON work again.
In db record, the field_lien_internet_rp_options contain now a:0:{} and all is as designed. But I don't know what s:32: is related (option of CCK linkfield for sure but which one ?) ans I don't know how to do a MySQL query to replace it in the db after migration because this data is in a blob.

New migration on another server and errors are back : but I found the way to modify blob content like this:
update node__field_lien_interne set field_lien_interne_options=replace(field_lien_interne_options, 'a:0:{}', 'a:1:{s:10:"attributes";a:0:{}}') where field_lien_interne_options like '%a:0:{}%';

I just need to put the replaced string as absolute, otherwise all records are affected in the table because of the replaced string is too much generic.

Drupal version                  :  8.6.14
Drush version                   :  8.1.15

Hello

since I do migration on D8.9 this issue disappeared.
The only thing noticiable, is the none mention on linkfield after migration.