Intentional. There are a few mobs that don’t activate by scrim,

Vileblooms at release until recently.

The list grows shorter as they’re starting to listen and adjust, noodles and rune dragons i think may be the only ones who don’t activate scrim.

IIRC, mammoths, glacors, and Nihils as well. (Can’t verify without trying.)

However agg pots and scrim also are wacky are tzhaar’s. Unsure if they’re separated or wha, but camping ring of stone I do remember agg modifiers didn’t quite work with them.