It took me only 8 attempts (including restoring the VM a couple of times) and a whole day to get the update to go through - most of the time I got the “uncommitted changes in frappe app” error which was a lie: Uninstalling the custom theming_tool app helped big time, after that I only had to apply the “cannot pickle module objects” solution from this thread here: Update fails - TypeError: can't pickle module objects
After dancing through the office a couple of rounds because of the success after that struggle, I was back to earth pretty quickly. Some of my customizations and my local translations are gone, and I get this error here straight after I login (as Administrator, there are no other users yet), and sometimes I get it when I go back to the desk too.
I already found the logs, but I would be glad if you could give me any hints in which file to look and what to search for. A first glance in the most recent log files did not show anything that caught my eye.
During the update I got one error a couple of times, which was asking for node V.10 instead of the available V.8. I tried updating that but there was no update available, it told me.