[error] AssertionError: Plugin definitions must have a class in assert()

Problem/Motivation

Drupal 9.5
Upgrade from version Beta 13 to 1.2
The Beta 13 is the last working version for me. Beta14 the error appears.

Recieving this :
[error] AssertionError: Plugin definitions must have a class in assert() (line 255 of /var/www/html/web/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php) #0 /var/www/html/web/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php(255): assert()