Setting up New Relative Rotation with some Static Mesh Actors in the Level Blueprint will have strange results if -90 is used in the Y Relative Rotation. Changing off of -90 will result in normal behavior, using -90.1 works normally.
Results: The Static Mesh Actor will spin around at sporadic intervals.
Expected The rotation to be consistent to the settings in the Level Blueprint.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-70322 in the post.