It sure is a great moment when your clowns take to their host anemone..... congrats
That anemone probably started moving so much after lights out because it wanted more light and started searching for it. Just a suggestion.... take that GBTA and manually put him on a high point in the rock structure (which is awesome BTW) And blast him with light and just a proper moderate flow. I'd bet it stayed put if it had a good place to wedge it's foot with the addition of strong light and moderate flow.