Yeah, of course I have daily backups of everything, it’s a rented server in a datacenter and that’s sending a backup each night to my server here at home - and I could restore the old database, copy my theme settings, then go back (I did loads of changes due to the change from MyBB to discourse for my Community ) and restore the Theme settings.
However, any time someone posted a comment in a thread which gets back imported to the Wordpress article, the theme went mad again.
What I initially did: I had to move my article comment forum to a new category after I saw that the plugin does not support sub-cats (they are not shown in the pulldown). But the new category was not listed in the dropdown, even not after disabling and reenabling the plugin. As there is no “refresh” button for the categories list in the dropdown, I went into the database and renamed the table “discourse” to “old_discourse”, reactivated the plugin and - yes, it created a new “discourse” table as expected. But still there have been no categories refresh.
So I deleted the new table again and renamed the initial table back to “discourse”. That seems to be a mistake.
Whatever I did, something gets messy resulting in the problem I’ve seen.
What solved it: I saw that deinstalling the plugin erased the two tables “discourse” and “discourse_version”, but the cache table was not erased. Also the discourse flags in posts_meta were still there. I need to erase all this in the database, then make a clean reinstall if the plugin - now it works again.
Finally it was my fault touching the database in the hope to trigger the plugin to see my new category. Not sure if the plugin need to take “its time” to present changes in the categories once it’s installed.