There are many factors, and probably several we don't understand. Sometimes my RBTAs bubble incredibly, other times they don't. Sometimes one side of an anemone bubbles, while the other doesn't. Of the 3 in the tank right now, 2 have bubbles today, while the other isn't. In short, a lack of bubbles doesn't necessarily indicate a problem.
In my experience, RBTAs are happy in strong lighting, moderate flow, and pristine water. Also, I've noticed that mine tend to bubble more in the days after feeding. It's also common to notice the bubbles mor prominently early in the photoperiod, but disappearing later in the day.