Topic on Manual talk:How to debug/Login problems

After I logged out as suggested by the above error, the wiki won't let me login and I get the message (again in red):

There seems to be a problem with your login session; this action has been canceled as a precaution against session hijacking. Go back to the previous page, reload that page and then try again.

Anyway, I added this line to my LocalSettings.php

$wgDebugLogFile = "/tmp/debug-mw20190724.log";

and saw that I'm getting database errors:

[SQLBagOStuff] DBError: A database query error has occurred.

[DBQuery] SQL ERROR: Table './wiki/objectcache' is marked as crashed and should be repaired (localhost)

So now I need to find out how to repair an objectcache...

It's a cache, probably you can just delete it and things will be regenerated eventually.

You can run query: REPAIR TABLE objectcache