At editor-time (ie, while using the editor and NOT in a PIE session), the Animation Blueprint's ability to read updated values appears to depend on what component of an Actor is currently selected, which is quite unexpected and confusing. If the root of the Blueprint is selected, updates work just fine. But if any other ActorComponent is selected then updates will not be made to the AnimationBlueprint. For a UProperty that is defined on an ActorComponent, the Animation Blueprint will only be able to read changing values while the root of the Actor is selected. If instead, the ActorComponent is selected, the Animation Blueprint will read stale data and thus will not appear to update.
See Attachment for repro project and video example of behavior.
Skeletal mesh updates, based on Animation Blueprint having updated state
Skeletal mesh does not update. This is because the Animation Blueprint is not able to read the updated values.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-91955 in the post.