There are 2 problems with Fixed Frame Rate.
1) *Not *using Fixed Frame Rate caps the FPS to 120. Why is it fixed at 120 and how do we unlock it? currently as you see it’s 120 FPS and 8.33 ms
2. Using Fixed Frame Rate option gives much more FPS and scene ms is much less. Currently 187 FPS and 5.35 ms. Why it costs 3 more ms if we don’t have the Fixed Frame Rate checked in?
Last but not least, when Fixed Frame Rate is checked camera movement becomes very weird. When you are moving to a direction using WASD and then stop pressing any buttons the camera stops meters away from the point you released the movement key which is really annoying. Also character movement becomes like Slow Motion (Adding the Third Person BP to project and walking around shows that).
These issues have been there for a long time in many UE4 versions.