You can clone with
Killing Floor is checking the wrong files when mutators are used on multiplayer servers. Instead of using the cached files from the server, the local version is checked in order to allow perks to be saved. As a result, experience is accumulated throughout a match, but is lost on map change or disconnecting from the server. This behavior is predictable and if the linux client has all the mutators that the server is using, then the client works as expected.
I'm also constantly losing the progress since I'm new to the game I'm not sure if the issue is known or something only linux users experience.
Is there a workaround for this? Such as downloading the mutators list manually or something?
yes, if you have all the mutators that are running on the multiplayer server in your client's file structure as if you intend to host the game yourself, then perks are saved.
This bug was closed because the issue concerns the game and not the Steam client. Please contact the game developer on their official website with this information.