Good bet 
That may happen because of the mixture of the two connection options.
We checked all possible scenarios. If you strictly follow this path: do not login but get a keycode; Performer also must not login (not even “accidently”) but only use the provided keycode. In that case, the message you mentioned can not be issued at all. Either the text of the message is different (which would point us developers to an entirely different direction!) or there is something very specific about your environment (like running VST Transit at the same time).
Did you at least succeed with the “signal left only” by using a Mono Input?
We want to help and really tried hard to reproduce your problem but so far there is no possible path to that message.