Why Advent Vega keeps losing Wi-Fi?
It could possibly be that you have a wifi time out enabled? Check the wifi settings carefully. Also, make sure the wifi sleep setting is diabled.

It could of course be a hardware issue (and probably is if it happens on multiple roms). It could be that the wifi card in the tablet 'Shuts Off' after a certain time, check online as this would happen to all owners of the tablet if this was the case.