Why is Thing getting staggered?

In quest 2.1 of the EQ, the juggernaut before Mr. Sinister, or perhaps all juggernauts, is staggering Thing after Thing Parries Juggernaut during unstoppable. It causes a weird effect of an infinite stagger that doesn’t even show up on the buff bar. Everything done is staggered even though Thing is immune. I don’t know how to attach a video but I checked the nodes and none of them should bypass things immunity.
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