I hope there are still active users around!

I am new to Ubuntu touch coming from postmarketos. Very nice first impression.

I had a hard way restoring OxygenOS 9 to my device but it worked. I then used the debian installer to install Ubuntu touch 20.04.

Everything looked perfect and I was proud to give this new toy to my son. But then we made a test call and the phone rebooted. Another one and it switched off immediately.
Then it worked but still made a bunch of random reboots.

Is that a known issue with this phone?