I guess you can plateau whilst gaining but it should only be brief. Action should be taken in response
If you hit your first plateau, up the calorie intake. The negative result could be extra fat gain for not enough muscle gain. I guess it depends on goals, you are prepared to accept extra chub you can could see greater gains long term.
Weight loss and maintaining muscle mass. My guess is a week of maintenance eating or even a binge as suggested! I'm trying to recomp a bit at the moment so hopefully I don't hit a plateau or lose too much muscle mass!