I have the same problem as the OP. Tried the server update button and have opened a support ticket UDR-564ZA
hope it can be fixed as it is reallly annoying, have even tried to use a redirect to see if it speeds up the downloads but to no avail.
[WP] Mr Treets
Clan Wolf Pack Tech Support Officer
Have you tried to recently update the server? If not, please try to as the SteamCMD update method was fixed sometime after the update went live, it was a last minute change by Steam.
If this doesn't work, the only way it can be fixed is by doing a Re-installation of your server with the Full Wipe checked next to it. The update is currently in an Event period so custom content will be broken if it uses custom Z.E.D.s or other specimens/entities that are not optimized to work with event Z.E.D.s.
Furthermore, if you're running any Muts, ensure that you have the latest version installed, the IJC Weapon Mut should be removed as it was made official and has been put into the official TWI game files.
Unless GS has another solution, this is the only way I could get my servers working, as the system files have changed. Ensure you backup your content before you attempt to do this. Once the server has been re-installed, then update Steam before attempting to utilize it. It will take longer than it used to do as the method that SteamCMD uses is quite different than HLDS for Killing Floor.
If you're having issues with your re-direct, check the [IpDrv.HTTPDownload] section and ensure it's placed properly, however, the redirect should have nothing to do with the Steam Update. o_O