Inaccurate prediction leads to fake weapon pickups
If you skim by a weapon (not sure if this bug also extends to items), the client will inform you that you have picked up the item (sound and message), but on the server you will not actually have the weapon. This is a widespread issue amongst many players.
If you jump to 1:14 in the demo, you will see me grabbing the rocket launcher and attempt to fire it only to have no rockets discharge. This easily happens many times during an actual game on this map.