[Marttt]

quick fix workaround is to remove the Tank skin from your local server,
since according to you is just one skin causing it, I would remove it

Try setting sv_pure and sv_consistency to 0 as well, I don't remember if this cvar still works.
You should mention what gamemode you are using (coop, versus, mutation), because some has the "RestrictAddons" attribute which may mess with your server

And since is localhost, maybe it behaves different, and SM doesn't support listen server

IMO maybe you have some plugin adding the tank skin to the AddFileToDownloadsTable
So try removing them all first