I wouldn't expect the connectors to be tarnished given how many times they have been unplugged over the last few weeks, but you might have a dry/cracked soldered joint on the back of one of the power board connectors then in which case the problem might go away for a while after they have been disturbed and then come back again when they settle down. If it happens again it would be worthwhile to inspect the joints on the back of the board where the connectors are soldered in - particularly CN1 and CN5 - and resolder any that look dodgy