This is a regression from 4.16 as I was not able to repro this issue in //UE4/Release-4.16 at CL 3514769.
Repro:
SK_Mannequin_PhysicsAsset
and double click to open it
Result:
There are no constraint axes visible in the viewport. Pressing the Constraint button does not change this.
Expected:
Constraint axes are visible.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-47035 in the post.