No longer able to view playback

Sorry for the delay in my response here, so it sounds like the cards are reaching their lifetime, I would put them in a computer and do a full deep format not a quick format and see if that changes anything. Sadly memory cards do have a finite life cycle and containers recording if you happen to use that can run through it a lot quicker than event recording. That’s one of the reasons that I personally use bigger cards so that I get more mileage out of them.