@direct3rand another update, it has happened again at the end of the round with the ak and the nightbird, but somehow it looks like it has todo with quick equipping the new things you unlocked, atleast this would explain why it does not happen that often anymore as I do not unlock so much anymore with higher levels.
So when I'm pressing quick equip after I unlocked new things at the end of the round, the chance that on the next restart (or sometimes even next round) of the game this type of vehicle/weapon has resetted is pretty high.