I would like to refer to this issue WeakAuras/WeakAuras2#2155 (and the related pull request #11) as I have noticed it still happening in the current version of WeakAuras 2 (3.1.8).

This visual glitch can be demonstrated using this weakaura on a priest https://wago.io/rqiF-wVdd

I have chosen the dummy targets in Sinfall (Venthyr sanctum) because the nameplates are nicely stacked

Steps to produce the glitch:

1. Choose like 5/6 dummies and start applying SW:P on all of them (remember the sequence in how you apply them)
2. Refresh SW:P according to the sequence, they should start glowing according to the sequence
3. When you reach the 5th/6th dummy, the first/second dummy should stop glowing
4. Continue refreshing according to the same sequence but watch the dummies that have stopped glowing - they will have the autocast shine visual for like one frame and then disappear

I have tried testing without the nameplate addon and the same glitch can still be observed. This problem does not occur if I am using other glow options - pixel glow or action button glow.