Steps to reproduce:
- create a wiki, say "test1". I create my wiki from a template, just in case it matters. I used the default settings for all the other settings
- delete the created wiki
- re-create the same wiki, "test1". The create form will return immediately (usually it takes some time) and will display the message: "Wiki "test1" creation failed: null.". The wiki is not created.
I haven't tested to check whether a restart of the server would allow to re-create wiki test1.
This is somewhat similar to
XWIKI-7775 but it's not the same issue (I cannot reopen), as that one was indeed fixed.