Issue: Having trouble editing wiki page ... getting vw_lock_contention

vw_lock_contention occurs if two edits to the same article are submitted at exactly the same time. The lock should expire after the first edit finishes saving, or after 5 minutes, whichever comes first.

After 5 minutes, it is assumed that the first edit failed for some reason, so the lock is released. I believe locks were introduced in 4.0.4, but the auto-release was not added until a later build of that version. You may need to upgrade if the lock is still not released after a long time.

Has persisted for weeks. How can we clear it manually for now; don't want to do a weekend upgrade ...

Delete all entries in the vw_lock table. Make sure you have not manually disabled any of VaultWiki's cron entries. There should be a task called "Wiki Clean-Up (Every 5 Minutes)"

Thanks. I'll check the cron.

Right after we cleared, a user got this error trying to edit; which might explain the lock issue.
What to do about that?

Yes, you are correct that the Fatal Error would cause an edit lock not to be released immediately (it should still be released after 5 minutes). Constantly receiving the vw_lock_contention for the next 5 minutes would bury the original problem of the Fatal Error.

In order to get that error, you would have to be using
vault/core/controller/dm/page/xf.php from 4.0.4 and library/vw/XenForo/DataWriter.php from 4.0.3 or earlier. These files are supposed to be from the same version.

Perhaps not all of the files were successfully uploaded to your server, or perhaps the package you got before was incomplete. Either way, constantly using mixed file versions can cause permanent damage to the wiki. If you have mixed versions like this, then you should download a new copy of the 4.0.4 package and replace your files as soon as possible.