Let me answer that this way, what was the cause of Debryune playing poorly the last game? He played in his customary position.
Players can have poor games unrelated to the position they played. Your assertion that he was found out suggest he played poorly because he played fullback. That's an illogical jump. He has had some poor games at his preferred position and some poor ones. All that suggests is that he had a poor game.
Just like every player has had regardless of position.
Fernandihno didn't play at RB. Again you keep making illogical jumps. It could very well be that Zabs inclusion at RB improved our attacking on the right. As a matter of fact think his movement in pro rd our style. Dihno was simply pulled for having already been booked. Simply a tactical decision.
This seems like a repeated question to score points.