The To Next button in the Animation timeline doesn't work consistently

In Persona, the To Next button in the timeline bar will randomly stop working if the user clicks it a few times.

I could not reproduce this issue in UE4/Main.

1. Open QAGame in editor.
2. Open the animation sequence ThirdPersonRun in Persona.
3. Pause the animation.
4. Click the To Next button in the timeline a few times.

RESULT:

The button may work a couple times (move the animation forward one frame with each click), then will randomly stop working.