This happens when you are over max allowed volume carrying capacity.
You were within capacity when you had the armor on, but when you took it off and didn’t immediately put another armor on you were then over max limit and couldn’t hold the armor itself.
Next time either have a second armor with you to swap out at the armor locker, or completely empty your inventory first to make room for the armor.
When the player is just in it’s underwear (no armor) it has a much lower carrying capacity for volume.
we can’t do much about your armor, but I gave you your Epic Rifle back
PS: Please use CB:Time to give us the servertime, not your local time. Can’t find much otherwise.