I have noticed the mixed feeling of muskaan as well but i think it has more to do with the story, as her character sometimes i feel is putting an act of being happy while she really isn't inside, like showed yesterday she still hasn't managed to move forward from her past which is making her life in present a living hell.
As for when it comes to rohaan, some of the scenes were OTT but he also is portrayed being this mixed feelings guy who doesn't know how to react sometimes IMO.
about the flashbacks where during the song sequence yesterday they had couple were they were happy and enjoying each other's company...most of the flashbacks were the scenes seen in the promos or atleast they had the same clothes on. As far as the other ones are concerned i am not sure they might once their love story starts from scratch. maybe the flashbacks will be show them gaining their memory back at one point. IDK nothing has been said about them as of now.