Yes welcome to the club mr_milo.
Yeah, don't worry about formatting it - it doesn't make a difference, nor doubtful there would be a problem with your card - it's the unit that is faulty.
Date/time should be still ok.
I have 2 units (front/rear) and only the rear unit is faulty and only randomly.
I swapped cards around (same problem), disconnected unit from base with plug straight to unit (same problem), put rear unit to front and front to rear (same problem with unit now at front), formatted card a couple of times whilst in unit and using PC (same problem).
I have come to conclusion to just pull my adaptor from cig connector and plug back in to restart unit as the trouble/time etc to send back for a replacement is not worth it imo - especially if a returned unit then does the same thing.
Use your Mobius as you say.