Occurs 5/5 times.
Details panel in Animation Montage goes blank when fields (Start Time, End Time, Play Rate, Loop count) are clicked in to update data.
This defect also occurs when clicking in the timeline in the Animation Montage details panel.
Regression does occur: Animation Montage data in Details Panel is updatable in //UE4/Release-4.27.2 EGL Live @ CL18319896.
Expected: Data in 'Start Time,' 'End Time' is updated.
Actual: Details panel appears to close and goes blank.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-150447 in the post.