I've 2 D235 and this has happened to both a few times. Both same revision and same firmware

They'll be working away and then one day all the recordings can't been seen it just says "No recordings" . It shows events and the image from the event but doesn't show that video if i click on it. I've continous recording on and can't look back over at any random none event time either.

I've them hardwired and set to continous recording and loop. SD cards arn't the cheap ones I got the higher end endurance for CCTV 

When I look as the SD card on the app it's full but loop is on and it says its good, and if i remve sd card and look at it on a laptop the videos are there. reinserting doesn't make them show up.

Formatting the card allows it to start working again, but I lose anything on it and even if I swapped them out or did backups to keep it going it won't have recorded anything after the issue starts.