Deep apologies on such a slow response. I've had some (non TurnKey related) crisis going on, whilst also trying to push ahead with the upcoming new major release (v18.x - based on the upcoming Debian 12/Bookworm).

Damn! I thought that we'd fixed all the GitLab issues in the latest v17.x release - seems that perhaps there are still issues?

Have you managed to resolve this or work out what it was related to?

If not, first I'd recommend that you check the usual things. E.g. make sure that you have enough free space on the system and there are sufficient resources for GitLab. GitLab is a beast, so you'll want bare minimum of 2 CPU cores and 4GB RAM, although 4 x CPU & 8GB RAM is recommended. Even if yours meets minimum requirements, it may be worth bumping resources if possible as that may resolve it?

If it's non of those (or you've updated stuff and still getting the same result), could you please share relevant log entries? GitLab related log files should be found in /var/log/gitlab. Alternatively you can view all logs live (i.e. see new lines as they are generated) like this:

gitlab-ctl tail

So probably the easiest way to get an understanding of the issue would be to open a shell and run the above command. Then try to recreate the 500 error in your browser.