Perhaps the api changed, here is the full log message: Sep 12 21:58:46 lumos NetworkManager: <info> Error getting killswitch power arguments: org.freedesktop.DBus.Error.InvalidArgs - Argument 0 is specified to be of type "uint32", but is actually of type "int32"#012
Are you still seeing this ? I believe it was fixed a while ago.
The log hasn't shown it since Sept 20th.