Setting up root motion in a sub instance to RootMotionFromEverything seems to cause the sub instance to evaluate, and override the notifies of the animation that was playing, which prevents the notify from firing.
Both animating characters play the same slot animation every second, which has a notify to trigger a particle system. Only the one on the right triggers. The file animtest422proejct.zip is set up in the same way, but both characters trigger notifies when played in 4.22.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-80431 in the post.