I performed a pretty massive 50,000+ node migration a few weeks ago (from Drupal 7.70 to Drupal 8.9), and just noticed today that some of the Text Filters aren't visible in content creation pages (in particular, Plain text filter, which is what I like to make the default for most fields).
I tried creating a similar filter called "Plain", but when defining the default filter for content types on text fields, though at least now the new filter is visible as on option from the select box, it won't save (it reverts back to Full HTML filter on save). Furthermore, the filter permissions page shows that something is awry as well...as I am unable to assign ANY permissions for the new filter or two of the migrated filters to any custom roles.
Clearly the migration didn't go smoothly. It took me 2 weeks to get ANY migration to work properly...so I really do no want to roll back and try again if possible. Is there any way I an fix the text filters and their respective permissions problem here?
I have full access to the server, mysql, etc. Is there something I should be looking for in particular? Or at least a DB model that I can copy?
Thanks in advance for your help.
EDIT: I just noticed that I can go into the individual user roles, and "see" the checkboxes that aren't showing up on the Permissions matrix (where you can select permissions for all users at once). Is this maybe just a rendering bug for the main permissions display page? Here's another screenshot: