We have located the cause of players using the medic perk causing players to disconnect from servers. This is caused by a package conflict in cases in which, for whatever reason, old packages were not being deleted from servers. We'll have a fail safe for this in the next Preview update but in the mean time servers can do the following to work around the problem:
Option 1: Delete your server and re-download the preview branch or download the preview branch to a new location on the host computer.
Option 2: Manually delete the contents the folder located in kf2server\KFGame\BrewedPC\Packages\Weapons\Knife
Either of these options will force the server to use assets from the correct location and should fix the bug where clients are disconnected from the server