Shared transition rules/crossfades are not usable by other state machines within the same ABP. Copy/Pasting these transitions to a new machine, create new independent shared transitions of the same name.
Create an animation BP.
Create a state machine with at least two states.
Create a transition between these two states and Promote To Shared.
Within one of the states, create a nested state machine with at least two states.
Create a transition between these two nested states and try to Use the previously shared transition.
Result: The Shared transition is not usable.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-82098 in the post.