How long have you had it in the tank?
What are the water parameters? (ammon. Nitrites, Nitrates, pH, Alk, etc) Make sure your tank parameters are stable and you should be good to go.
It is pretty normal for them to shrink and then puff up again…. I've had mine for over a year and it does this from time to time.
They are all different, my RBTA doesn't bubble either, but my orange flame BTA's bubble all the time. Each one is different and there is no rhyme or reason why they do what they do.
Cheers,
Ryan