Happend to be that i was training with a new guy (in for about 2 months) and he wasn't really comfortable with ukemi yet. So in the moment he grabbed my wrist he was already busy with preparing his roll. Sure did feel very fake in that way and i had the feeling i wasn't learning very much. (well putting away my ego to give this guy a chance to learn ukemi was kind of hard for me but my waza didn't improve by it)
Maybe your "waza didn't improve by it" but I bet in giving up your pre-thinking about what you wanted to work on in class and focusing on the actual human being you were partnered with your overall Aikido improved. Because being present in the reality of the moment, not in our hopes or wishes for reality, is what a martial art offers us.
And I'm not being flippant in saying this. I really believe sometimes that IS the lesson when class doesn't go the way we expect.