Thanks for all the input and suggestions. Some interesting points there!
However, I think I fixed the problem, though. (But will continue to watch it, of course).
I spend some time to check all the connections and it appeared that one of the solar phases was not fully tightened at the circuit breaker (was able to give it another quarter+ turn!).
After tightening that screw, system has been working flawlessly!
As of the question about line voltage. It always hovers around 124V so that’s normal for here.
Thanks all! I will report back if there is anything new.
(Tesla was scheduled to come over on Thursday. If things are still good on Monday, I will cancel the call.)