Yes you need to feed it since it is severly bleached. 2-3 times a week would be good since it doesn't get much of its nutrition from the lights atm.
There is no scientific answer as to why/what cases the bubbles to appear or dissappear. Some say stress, or lighting, or whether or not a clown is hosting, but there isn't really a definitive answer. The presence or lack of bubble's shouldn't really be used to judge health of an anemone.