If your perks have appeared to reset to 0 completely, it is likely that your game client is having trouble reaching the Steam backend where your stats are saved. This also includes those servers (all or in part) being down for some time.
- This issue should clear up over time, but try closing the game and re-launching it to force a new connection
- Try loading a map via the command line console and see if that allows perk progression
- Bring up the console with the key: F3
- Type: Open KF-BurningParis
- And hit Enter
- Play a few waves and see if progress is saved
- If progress is saved, try playing online again
- If the issue persists try doing a steam file refresh - instructions can be found here: https://support.killingfloor2.com/en/steampc-knowledgebase/article/manual-steam-file-refresh
If some of your perks have gone to 0 but not all of them or they appear to no longer be progressing at all it is likely that your stats have become corrupted and the game is failing to update them. The only way to fix this is to reset your stats on Steam. You can trigger this by opening the game console ( ` ) key by default, and typing:
- resetstats "YourSteamNameHereInQuotations"
This will reset your perks to 0, and you will be able to progress normally from this point. We are not able to manipulate your perks to a previous point.