Alright, changed everything you told me and re-ran the upgrade with disabled listeners again and it went through this time. Then I enabled the listeners again. So far it seems to have worked.
Error 1: I have installed XenPorta 2 from Jaxel and the Home page (where the portal resides) now displays a generic error:
An error occurred while the page was being generated. Please try again later.
Nothing in PHP or XenForo error logs though
Error 2: I try to open the Wiki (navigation entry to domain.com/wiki/) and it tells me "The requested page could not be found."
Also neither PHP nor XenForo errors
I'll try to run the upgrade again with a fresh test copy of my production board as soon as the new version is out
Thanks and keep up the good work!
Edit:
Regarding error 2: I've now seen that it automatically redirects me to domain.com/wiki/ although I'm on test.domain.com. Changed the Wiki Base URL (and it's saying "in progress" since like 5 minutes after I saved) but it works now.