Carrot is under voltage at shore current connection

Hello, I’m sitting on Corsica on vacation with my T5 camper, in which is built a shore power connection with charging ditch for the supply battery. Also a 230V inverter. So the day before yesterday I had the problem that when a consumer switched over I probably broke the inverter, which is exactly there I can not judge. Turn it on still does, but goes on fault, sissions in the wiring are i.o…. Soo well, then I don’t use it anymore.. Then close I stop at shore current, I don’t need an inverter. Now I notice, when I touch the coupling that this is slightly under voltage.., I plug off the shore current, everything again i.o. ?? Does anyone have an idea how this can come about? It is all grounded, the cables are properly connected, the system worked already 4 years without problems ! I have meanwhile completely disconnected the inverter ! Can the problem of lack of supply of the shore current socket coming from the campsite ? Vllt. bad earthing ?? Do you think it is worrying to use the land current anyway ? The battery load, the charger shows no errors and does not become excessively hot … About Andtworten I would be very happy! Thank you !