for some reason I had a permanent 4th weapon in the third slot (MXR-15 rifle). I've played with Samantha's Drawing relic
– you can safely replace the weapon in this bugged slot from a wall buy
– however picking up any weapon from the Mystery Box or TEDD reward will break the slot and force you to drop the weapon
– every round, your rarity state on this slot resets. The PaP level stays though
– the relic does not swap this weapon, as I said it's permanent until the slot bug is active. the 3rd regular slot weapon is being swapped as intended
– I had this bug twice during the match, however I don't really remember how to recreate it