Hm, usually happens when an ammo crate is on its max capacity.
Maybe the car does not initially allow to hold weapons (does not have "transportmaxweapons" flag assigned?) - cant check thatone since we have no un-pbo tool yet.

Also, ever since, lag has affected the behavior of damage dealt, get in/get out vehicle actions, and the gear.

Lets wait what the other users say.

This happens even if I do not already have a primary weapon and I'm not moving anything else, only trying to take a weapon. And it's not always weapons, sometimes items like binoculars or weapon attachments too.

Reproducible. Up-Voted and Monitored.

Issue was looked into and fixed.

Thank you for reporting this issue to us. We appreciate it, keep up the good work and help community and developers to build better game for all.

Mass close.