Why has my ipad started deleting all old videos when I add new ones?

It's only just started doing it. Whenever I now manually add a new home video it has started to wipe all the old ones and replace them simply with the new one. I have always had it set to manually manage both music and videos so it should not be a syncing issue. It's an Ipad Air and has the latest software update installed.

As home videos make up the bulk of the content of my Ipad it's incredibly frustrating that I have to wipe everything and install it all again if I simply want to add a single new video to my library.

Any advice or guidance would be appreciated.