The “workflowengine” log line here is a red herring, it is just the latest app (sorted by alphabet) and already the next step (fixing oc_filecache entries) is running which is the one that fails.
As a workaround, updating via occ upgrade should mitigate this issue. Or try the patch from @nickvergessen
Using the patch now hangs at “This Nextcloud instance is currently in maintenance mode, which may take a while. This page will refresh itself when the Nextcloud instance is available again.” for about 30 Minutes…
Adjust config/config.php and replace:
'maintenance' => true, with 'maintenance' => false,
Also try this patch in addition: https://github.com/nextcloud/server/pull/6047/files
• config.php is changed
• path_hash is added
• #6034 is applied
Result: “This Nextcloud instance is currently in maintenance mode, which may take a while.”
P.S: I can’t run "occ upgrade"since the plan at the ISP doesn’t allow SSH
Then the config.php change was not saved, or someone else started the update?!
• it was saved!
• No, no one is doing anything now
Well this is only shown when maintenance is true.
Maybe it’s cached? Disable memcache etc for the moment
Sorry, I have no idea how to do that.
I now have to revert back to the latest backup (I simply don’t have the time to poke around, especially with me being a numb) and try to avoid updating NC. I thought the … old oc-days were over where the best advice was: “Don’t update!” :o((
occ upgrade did it for me. But now I got: Einige Dateien haben die Integritätsprüfung nicht bestanden.
I thought before “better make a backup” but then I thought: “naah, the upgrade from 10 to 11 and from 11 to 12 was smooth, there shouldn’t be a problem”. Big mistake and I aged for years last night 
Well that is expected, since you changed the files following the steps above. Just ignore it until the next release 
No change with version 12.0.2
Yeah, sorry about that 12.0.2 was a quick fix release only fixing one specific problem, you will have to modify it again and ignore the warning until 12.0.3
I tried to update to 12.0.2 and now I got the error:
“Delete old files
Could not rmdir /var/www/nextcloud/updater/…/apps/workflowengine”
soooo, what to do? I can’t do anything, I only get a blank page with “Update in Progress.”
push
guys, I need it running!
push
push
I had to restore a backup.
I would like to update it somewhen! how can I do this???
Push
I would like to update it somewhen! how can I do this???
Push#2
I would like to update it somewhen! how can I do this???
A patch will be in 12.0.3, either wait or apply it manually: https://github.com/nextcloud/server/pull/6148
So this Update will solve the problem with ““Delete old files - Could not rmdir /var/www/nextcloud/updater/…/apps/workflowengine”” during the update process?
It seems to fix the initial report. Not sure if your error is related. If you really need and want to upgrade, I would use the manual upgrade:
sudo -u www-data php /path/to/nextcloud/occ upgrade on your terminal (www-data is your webserver user on debian/ubuntu and can be different in other distributions)