Unfortunately I have never seen that problem before It happens from time to time that SteamCMD does not recognize updates in beta branches, but the validate parameter usually does the trick in these cases... does it help if you delete the server files instead (just the Data folder, for example), then execute the update?
negative .. complete fail (even if i remove data folder frm server). this problem happend before .. every time actually, but goes away 30 min after u list update. this has been over 3 hrs now. i never had to run validate command actually