Not really strange. I had the same problem with my black ocellaris pair. At first they showed no interest in the bta so on the third night i did the flash light trick and both were hosting. The next morning they were not hosting any more. So two more days went by and they did not show anymore interest in the bubble so I decided when the lights were out that I was going to attempt the flash light trick again aided with a net too shoo them close to the anemone but not actually inside the anemone. It worked the second time around as they both now host and protect the area around the anemone. At night I believe the clowns are looking for added security, as the net mimicked a predator, so they take to the anemone more readily than if I were to attempt this when the lights were on.