It’s probably of little comfort to you but I reset my phone to get back to something that works.
I have previously complained on here about the default user and so a reset took mine back to 3.2 as that’s the newest version with nemo as the user. But it meant that I had to go through these loops to bring it up-to-date :- 220.127.116.11 → 18.104.22.168 → 22.214.171.124 → 126.96.36.199 and finally 188.8.131.52.
I didn’t do anything in between those updates apart from when I went from 3.2 to 184.108.40.206 as it had reset the timezone to Helsinki and so I got the dreaded ‘Can’t determine files size’. As that’s the first check it was an easy enough fix. One of the other problems I’ve had previously is that the phone would only ring once and then while the call was still awaiting an answer there would be no more ringtone. My wife called the phone to check and it rang properly. I hope that continues as I restore all the other stuff and apps that need to be re-installed.
As usual there’s the problem of a backup / restore not working properly but having had problems in the past I have documented all the steps necessary to get back to a working device such as not storing any contacts or calendars on the phone. They’re all stored on my Nextcloud machine. While the calendars now work without any intervention, the contacts don’t. So I’ll have to fix that.
Sorry I can’t be more encouraging but at least I now have a working phone - until the next time!