Did your electrician check the connections in the power distribution panel in your 5er?
We had a problem where the neutral buss and the neutral main wiring were all loose inside the trailer power distribution box. Caused all kinds of strange problems.
X2 about getting a surge protector. We identified the 30amp service was reversed polarity at a Moab RV park we stayed at this past fall. Maintenance guy came by and found all kinds of problems with a repair done a month prior on the pedestal including the personal hazard ground was not connected. Found that one when he got zapped at the pedestal. Who knows how many folks were "lucky" and didn't get hurt with that one. Thank you was a free nights stay