I want to add the following.
Yesterday during the day I could install and run everything, but because I want to start it from SSD I had to install it a lot of times.
The problems started in the evening. That is when the troubles began and I couldn't start OMV5 again.
So something happened during the day.
Now I will go back to OMV4. I still have the image and this is working.
Yes, it seems that something happened yesterday. We are all experiencing the exact same behavior: no access to the web gui and after setting a port in firstaid we get the 502 bad gateway nginx error. We used different raspbian busters lite images so the problem doesn't seem to be related to this.
It happend yesterday during the day. Anyone knows of changes to omv 5 that were made yesterday maybe ?