I also have vctf server and players can't kill each other.
The server reports the error message:
It is repeated countless times...ScriptWarning: UTVehicleCTFGame_Content vCTF-Containment.TheWorld:PersistentLevel.UTVehicleCTFGame_Content_356 (Function UTGame.UTGame:MatchInProgress.Timer:0079) Accessed None 'PlayerReplicationInfo'