Totally hard to say, especially since the others are fine. I have found that sometimes they just do... If you lose the whole bloom (don't give up yet, sometimes at least a flower or two makes it) repotting might be in order... timing in the next month or two would be fine, you're getting new growth. How long since the last potting? I have found that sometimes it'll do that when the roots are not happy. But sometimes I just don't know. Here's wishing you the best for the rest of them!