I bookmarked this thread, as it was important to me. I must admit, I haven’t read all of the posts, but I want to report something possilby relevant, This issue has been affecting me since September 2020 when I bought an FP3+. I quickly found out, it had this issue. My last “support request” update from FP is dated early December 2020, which is outrageous (they should be ashamed).
However, one of the things they asked me to do what to request a new SIM from my provider, and a while ago I did. I got a new one a few weeks ago and put it in. Now, the trouble is, my phone is more a pocket computer than a phone and I don’t get called a lot. But today, I got two calls, as in you know that outdated technology kind of thing, non-VOIP stuff, and they both worked. I wasn’t expecting that at all, and was very surprised I could hear the other end.
Anyway, slightly anecdotal, and not sufficient to say “we’ve seen the light”. I am also on the latest Android 10.