MP5 - Every single one I've picked up has either been bugged or becomes bugged very soon after picking up and causes big problems.

Majority of the time when I pick up an MP5, it comes with the bug where the mag won't drop and only one round will load into the chamber. Mag gets stuck in the gun, etc, typical to the already known problem, but with the MP5 so far, it's been 5 out of 6 times that I have picked one up.

Dropping Items - this seems to only happen with guns and mags, but has happened to me specifically with the FN 45, the MP5, and the Skorpion. If I drop the gun and then drop an accessory on top of it in a stack (mag, supressor, etc), I won't be able to pick any of it back up for a period of time or permanently. The prompt to pick it up will appear, but pressing buttons does nothing. If I bring up the inventory menu and try it that way, the buttons still do not work yet the bottom row of options once a gun is in your hand still changes as if the gun is indeed in my hands. At that point though, the inventory menu no longer works at all and all I can do is back out of it. After backing out of it, the items on the ground stay bugged, sometimes resolving themselves and I can eventually pick them up again. If I mess with it too long though or walk over the stack of items, my character begins snapping around the room of wherever I'm at.
During one of my processes of trying to get an MP5, I dropped a 45 mag that was empty, but now it reappears in my inventory every time I spawn into a server. No matter when or where I drop it, it always reappears. I will update that if anything changes with the presence of that mag.

Mag/Round Count - the loss of rounds now happens at random it seems. I spawned into a server after having left with a full mag in my gun, and it was down to 9 rounds after rejoining a new server. I haven't shot that gun since I fully loaded it a full server cycle ago. So now, it seems that rounds are not disappearing after loading mags within your inventory, but whenever the game feels like teasing you and making you lose rounds. I also noticed that during the original mag loading/round losing issue, sometimes the lost rounds will reappear in your inventory in a count that does not match what is missing from your mag inside of your gun, leaving you with a new stack of rounds in your inventory.

One Known Gun Bug, Tip To Avoid- If you have the FN 45 or the CZ pistol, do not use "B" to combine and load a mag. Keep the mags in your inventory, gun in hand, and load the gun with "Y." Every time I've loaded a pistol by combining it with a mag in my inventory, the pistol has immediately bugged. The 45 does the mag in gun but only load one round via chamber routine, and the CZ pistol won't show a mag and will not load in the chamber and the slide stays locked back.

My current workaround for these is just to not mess with the MP5, not stack guns or gun accessories, when I load mags- take the mag out of my gun and load them ALL in my inventory, and with the pistols, do not load them with the "combine" command.