Picking up live IEDs or C4 will often take a player's weapons away. I don't know how a player's character appears in 3rd person in this state, but their gun's viewmodel disappears and they are unable to switch to any of their other weapons. Seemingly, the only way to get out of this state is to pick up a dead player's weapon up off the ground. This bug has happened to me 3 times, and gotten me killed once.
I believe I saw something similar to this. I picked up a live frag grenade thrown by a bot using F to try and throw it back, but after grabbing it my character's hands disappeared and I was stuck unable to throw the grenade away after releasing F as it is meant to work, even spammed clicking but nothing happened. It promptly exploded and killed the remainder of our team
Possibly related, picked up a non-live grenade from the ground. When I tried to prime it, the same thing happened until I switched weapons. Essentially, releasing the mouse button would not throw the grenade and I just got sort of stuck with no weapon equipped.