I now got a new BV9000 Pro HD phone. Yes: I did the mistake and bought another Blackview device.
The problem remains.
However, I have found a workaround. Set the phone to 3G only mode, and now the problem with restarts have vanished. The problem seem to be with some of the LTE features (perhaps VOLTE?) Or cell reselection / power save parameters.
The issue is now that I have an 3G only phone. Admin: Will this be fixed in an future update? And, you stated 6 MONTHS ago that Android 8 will be available soon?? When is it coming out?? / Unsatisfied customer
Since I have no issues like that on my device please try if this will be solved by a factory reset