The likely scenario here is a site admin was browsing through the "Appearance > Themes" list and the admin activated one of the CommentPress themes without having the CommentPress Core plugin activated.
I think we should do the following:
- Network-disable the
commentpress-default and commentpress-modern themes so these themes are no longer allowed to be shown in the "Appearance > Themes" screen since they only work with the commentpress-core plugin. (I've just done this, so no need to do it.)
- Remove the
commentpress-theme and commentpress-modern themes from /wp-content/themes/. WordPress only stores the theme slug in the database, not the absolute path to the theme directory, so we should be safe. (I haven't done this yet. Wanted to get some confirmation before doing this.)
Sites that have either commentpress-theme or commentpress-modern should have the commentpress-core plugin already activated. It's not possible to activate just those themes without receiving a fatal error as evidenced in the last few tickets (#13715, #13656).
To be sure, I ran a WP-CLI command to see where both themes are active:
Sites where commentpress-modern is active:
+---------+---------------------------------------------+
| blog_id | url |
+---------+---------------------------------------------+
| 1603 | https://disswrkshpf13.commons.gc.cuny.edu/ |
| 1682 | https://cunyfemtech.commons.gc.cuny.edu/ |
| 1800 | https://sicelidas.commons.gc.cuny.edu/ |
| 1921 | https://jk82.commons.gc.cuny.edu/ |
| 2241 | https://techlitfrench.commons.gc.cuny.edu/ |
| 2273 | https://jitpcomments.commons.gc.cuny.edu/ |
| 2309 | https://fragments.commons.gc.cuny.edu/ |
| 2314 | https://techniques.commons.gc.cuny.edu/ |
| 2358 | https://wgs10016.commons.gc.cuny.edu/ |
| 2748 | https://malswrites.commons.gc.cuny.edu/ |
| 3944 | https://ivanhoetest.commons.gc.cuny.edu/ |
| 4004 | https://tristengoodwin.commons.gc.cuny.edu/ |
| 4332 | https://stefanomorello.commons.gc.cuny.edu/ |
+---------+---------------------------------------------+
Sites where commentpress-theme is active:
+---------+--------------------------------------------------+
| blog_id | url |
+---------+--------------------------------------------------+
| 1063 | https://promockup2.commons.gc.cuny.edu/ |
| 1271 | https://deathofthetermpaper.commons.gc.cuny.edu/ |
| 1313 | https://amstprosemsp13.commons.gc.cuny.edu/ |
| 1394 | https://thesocialpaper.commons.gc.cuny.edu/ |
| 1491 | https://librarians.commons.gc.cuny.edu/ |
| 1506 | https://eshtestcac.commons.gc.cuny.edu/ |
+---------+--------------------------------------------------+
All sites have the commentpress-core plugin activated. (eshtestcac.commons.gc.cuny.edu has another unrelated error, but that site is marked as deleted so I'm not going to spend time debugging that site.)
One other thing I encountered is if a site has the commentpress-core plugin activated, the other bundled themes for CommentPress (commentpress-theme and commentpress-flat) are not visible under the "Appearance > Themes" screen. I've just added a commit that will allow these themes to be activated if the commentpress-core plugin is active: https://github.com/cuny-academic-commons/cac/commit/1e1ef9c7da7f13b6e75574d6261280434bf018c3. This should properly solve #12573. I've also reported this issue to Christian (who maintains CommentPress) here.