Missing Dashcam Files and Date Out of Sync

At the beginning of every month I format the SD cards in my dashcams as I was advised by a few people this may prevent recording issues. 

Tonight I noted that files 201 - 205 were not listed on the front facing dashcam, (Roadhawk DC2, hardwired with Parking mode activated) . Those files would have included the journey to a garage, and parking up outside, possibly more. 

The rear dashcam (Transcend 200, hardwired but i only comes on with ignition) was displaying the incorrect date and time; 27 Nov 17 06XX, instead of 3 Dec 17 14XX. I formatted the card before I discovered the missing segments on the other memory card, so cannot cross reference the missing segments with the incorrect date and time. 

Previously I've had issues with the Roadhawk not recording correctly - it would miss a segment out, but the recorded file numbers would still run sequencially, hence formatting monthly. 

And I've had occasions where either, or both dashcams are displaying the incorrect time, but that was normally due to the clocks going back or forward, never hours, or days out. 

Any suggestions as to why this has occurred?