I would think the longer you were with a previous partner, it would be more difficult to mesh with a new one, no matter what previous success you had.
Timing of spins, throws, footwork, lifts, jumps all of which was intimately known with your previous partner are totally new. If you are focused on syncing and looking for new cues on timing - you don't have enough extra effort to emote chemistry.
Since the man has responsibility for safe lifts, timing of throws, I imagine Eric is concentrating on those and may indeed look wooden.
Both have to learn different approaches to lifts - since they each have signature moves.
Personally I think it will take them another year or more to begin to show personality