I started to notice, that when random map rotation glitches and starts a deathmatch round instead of coop mission your level progress often resets. What i discovered lately is the fact that it can reset your character to a state in which he was at the random (but very long) time ago. Just yesterday i had almost all possible researches, all weapons exept arracandora and level 68. I tried to create an assimilation game to just look at the maps. After i quit game and relaunced it i found myself without ALL things i had. So there's two things: 1.If you want to play versus modes. Try load different character before. 2.To developers: please at least remove bug which swithes your coop game to a deathmatch game.
Better choice for such a bugged game would be a complete save system overhaul. Now game has saves and backups. I don't know how often game make a back ups but it looks like VERY rare. All the rest of the time game owerwrites your main save, with risk to completely destroy all your achievements. So my suggestion is, that game must have 5-10 save folders, when limit is reached - oldest save must be overwriten. In addition each save must have a txt file with all stats of your character. so if your saves are spoiled you can go back at least several game sessions back.