VC 3.1 500 valley

Since a while I can't seem to get a proper bedmesh (nor proper first layers) on my vc 500. It was working fine now for 1.5 years. Also I upgraded to 3.1 + added a CF gantry, however I don't recall if this was exactly the time this started or if it happened later on. Screenshots show mesh after levelling with a super pinda on a self-made pertinax sheet & original RR PEI. I'm somehow a bit clueless at the moment, I was suspecting the pinda as it sometimes stopped working on higher bed temps and ran into the nozzle, but not sure if that is really the culprit here. I can't imagine the aluminum base would sag like that? Any clues on that one? thanks.