Yup, it's bugged. Many debuffs (slows, freezes, clouds from hive wizards, missiles from colossus) and some buffs also wipe out classy restoration instantly. Been trying to get the attention of Bungie on this as have some other people who have posted but as far as I can see it's not in the TWAB or on the list of known issues yet and hasn't been acknowledged. It's annoying to have a last tier artifact mod that costs 6 energy on your class item AND your class ability (especially on warlock) cooldown basically negated because some minor debuff, buff or mechanic (like the GOA engrams) overwrite your restoration suddenly. Hope they see one of these posts soon, investigate the bug, and get it fixed soon.