Add custom block with Content Translation active - get PHP error

I have every Drupal Core module enabled on my test Drupal 8 site at the moment, since I'm looking at help text for another issue.

I went to /admin/structure/block, and clicked "Add custom block", which took me to /block/add, where I chose the "Basic Block" type, and that took me to /block/add/basic.

I typed in a few words for the description and the body, and clicked "Save".

My block was not created. I got a fatal PHP error:

Drupal\Core\Entity\Exception\UndefinedLinkTemplateException: No link template "drupal:config-translation-overview" found for the "custom_block" entity type in Drupal\Core\Entity\Entity->urlInfo() (line 176 of core/lib/Drupal/Core/Entity/Entity.php).

Furthermore, when I went back to admin/structure/block, and clicked on "Custom block library", that page now doesn't work, with this fatal PHP error:

Drupal\Core\Entity\Exception\UndefinedLinkTemplateException: No link template "drupal:config-translation-overview" found for the "custom_block" entity type in Drupal\Core\Entity\Entity->urlInfo() (line 176 of core/lib/Drupal/Core/Entity/Entity.php).

(Oh, I guess that is the same error message.)

Anyway, it seems to be an interaction between the Custom Block module and Content Translation, so I've filed it under Content Translation module and tagged with D8MI.

And it's critical because my system is now unusable for custom blocks. "drush cr" does not fix the error.