My parents’ house had a similar issue. We checked, poked and prodded. Finally found the problem was a tree growing into the feed line between the transformer and the house.
i wonder if that might be it as others in the area are having the same issue- and it began aroudn the same time- so that would seem to indicate something out at the line instead of inhouse- If the next electrician can’t find an issue, we’re gonna have to call the power company i guess-