i don't have this issue on Altis Life or on the COOP servers i play on

But on breaking point it's not only the Backpacks that do this

1. if i switch Clothing (I play the None Class) it empty's my vest partially

2)when i switch vest/belt it empty's my Backpack partially normaly it's about 50%
of the backpacks content that disappears and it's always my ammo if it's in there

3. is when switching backpacks is sometimes empty's my clothing fully