If you use dregs of lies rank 3 stacking effect with permanent simulacrums, the dregs will stack from the casting of the simulacrum (normal) but once the stacking reached 100 and dropped off it wont stack ever again until you summon new simulacrums.
I wanted to use it with masquerade (after all the simulacrums do the damage on this set, so using a pet focused gem made sense) but for now it doesn’t work the way it should.
I think a similar issue exists with monks and mystic allies.
Removing and adding the gem back doesn’t help. Only summoning the pets again allows to stack anew which makes me think that there is a flag on the pet that isn’t removed when all stacks have been removed from the player (probably because simulacrums and mystic allies are unconventional pet that can potentially cast player abilities and/or don’t show up in the follower/pet bar). I would guess the same issue might exist with sentries and the marauder build, but since sentries have limited lifespan they naturally get summoned again and as such they can stack normally