This was an old glitch originally done with the Stroudie Vaktovian Weapons before they were updated to have reload animations. This glitch was preformed by having at least two guns in your backpack, and hitting backspace to attempt to drop it. Normally, anytime you did this, if not touching another person, the gun would seemingly glitch for a split second, then be held by you again, showing that is must drop right above your robloxian. To do this glitch, you hit backspace while holding one of the guns, then quickly click another gun. You will pick the first gun up again, but the two handed hold you normally have with the guns will be gone, and you will hold it in one hand.
Recently, with the addition of redesigned weapons that came with the opening of SMO 2.0, this glitch has been able to happen if there is server lag, and an individual pulls out their weapon from their starterpack quickly after spawning, causing it to break, be held in one hand, and be unable to fire any shots, thus requiring the individual to reset to have a usable gun.