When player leaves to the lobby while they still "control" dead unit (waiting for respawn timer), their body sinks into ground and their gear disappear with it.
This is a long going problem for loot-oriented multiplayer mission with bodies disappearing with all their gear when players leave the game. (by going into lobby, disconnecting, crashing, getting kicked, etc.) It is an issue in players vs players multiplayer games where players leave the game after being killed so their killer couldn't loot their body and take their weapon.
In general, the behavior of body with all gear disappearing into the ground is a problem for missions that are oriented on looting.
This has been an issue since at least ArmA 2
Repro mission & Video attached {F23330}