It seems like this trinket is not working correctly at all. From what I can tell it simply doesn’t apply the “Persistent Shield” effect on many of the spell casts. I’ve tested it with single target heals, prayer of healing, and holy nova. The behavior is extremely inconsistent. It will often apply the buff to members of my party, but not myself. I have also noticed the buff being removed prematurely as well. Tested with no additional addons running as well as my usualy addons, same exact issues.
Video displaying one example of the problems during holy nova casts below. You will see me spamming nova and if you look at the party’s buff icons you’ll see its removed immediately from myself multiple times and the buff refreshes only sometimes on party members.
As another user pointed out in a similar thread, it looks like the bad behavior here is that when you heal a different target, it removes the shield from yourself. AOE heals are probably doing the same thing. Not sure if that explains all the error cases, but it seems pretty consistent with my testing as well.