Mine have done the same in the past and they weren't sick or in pain or distress.. they seemed to be ok and weren't having any problems or grunting like they were in pain or hunched over. Did you note any signs of distress with your bunny? Sometimes mine makes bigger poohs at times! other times a bit smaller. I think it's off how much mine have been eating.. if they are outside eating grass like crazy then they have abit bigger pooh with my girls that go out..
Vanessa