Residual database creates error messages

After fiddleing a little too much with one of our subwikis (especially renaming), we seemingly have a zombie database. All our subwikis are functioning as expected (at least as far as we can see, even the renamed one). Still, when checking for upgrades for all our subwiki extensions from the main wiki admin section, we get a bunch of messages like these:

Starting job of type [upgradeplan] with identifier [extension/plan/]
Resolving extension [Office Importer Application 13.10.5] on namespace [<OUTDATED_SUBWIKI_NAME>]
Since database [<OUTDATED_SUBWIKI_NAME>] needs to be migrated, it couldn't be safely used! Please check your configuration to enable required migration for upgrading database from version [1008010] to version [130406000]
[...]

where <OUTDATED_SUBWIKI_NAME> is an intermediate name of the aforementioned subwiki.

Obviously we did an upgrade recently, which after some hard work, finished as expected and runs smoothly now for the main and all other subwikis. Before the upgrade we occasionally had error messages concerning this zombie subwiki as well.

What would be the best way to get rid of this database? What could be the reason for such a left over? Are there any potential dangers involved in deleting the database in mysql or better, where should we erase it, to get rid of the messages without causing trouble elsewhere?

Any suggestions and hints much appreciated!

Best regards,
Björn

I would like to resurrect the topic. Does anyone have an idea, or suggestions on how to tackle this situation. Is there any harm to be expected from just deleting the database? Or can someone point me to the documentation to read about the topic?

We now started the experiment to just delete the database on MariaDB side. When checking for extension upgrades, we now receive the errors:

Starting job of type [upgradeplan] with identifier [extension/plan/]
Resolving extension [org.xwiki.platform:xwiki-platform-watchlist-ui/11.6.1] on namespace [<OUTDATED_SUBWIKI_NAME>]
SQL Error: 1049, SQLState: 42000
(conn=11) Could not select database '<OUTDATED_SUBWIKI_NAME>' : Unknown database '<OUTDATED_SUBWIKI_NAME>'

When we check the Watchlist Application, which of course is uninstalled in all our actual subwikis, then it says in the extensions module:

Installiert in den folgenden Wikis
    <OUTDATED_SUBWIKI_NAME>, von Unbekannter Benutzer am 08.10.2020

Could someone please point us to somewhere we can find a hint for the source of these hidden references? We just have no clue where to look for them.

Finally, we simply decided to recreate a new subwiki with the <OUTDATED_SUBWIKI_NAME> name and rightaway deleted it afterwards. That solved the issues. No more errors in the logs and Extension Manager UI.

Feels more like an effective hack-around, but definitely solved the issue.

So, yes, it resolved the issues with the extension manager UI, but…

When creating a new subwiki, the logs start with:

Starting job of type [wikicreationjob] with identifier [wikicreation/createandinstall/testSubwiki]
SQL Error: 1049, SQLState: 42000
(conn=6692) Could not select database '<OUTDATED_SUBWIKI_NAME>' : Unknown database '<OUTDATED_SUBWIKI_NAME>'

I am still wondering what is causing these errors and if this affects the performance of our wiki potentially causing future crashes.