Ahh, that must have been it. We just shrugged it off and blamed it on a disgruntled admin who has been having complaints and whatnot, so we didn't think much of it. Will keep the bug in mind, though.
Here is what happened, in order to get above x1, you must survive 3 waves of a type of unit. First is Peasants, then Bandits, then Weaboos etc. If you die on any wave other than the 3rd one, you get kicked and lose your multiplier. This will also happen if you join a server during one of the first two waves where you cannot spawn.
The reason you don't get kicked if you die on the 3rd wave is because everyone respawns at the end and a new enemy will start and your multiplier goes up.