If instanced stereo rendering is enabled, then all debug rendering is drawn twice - once normally, once distorted in black.
Open the VR template
Set the “GrabSphere” to no longer be hidden in game
Compile and Save
Play in VR Preview
Notice that there is an extra Collision sphere that is shown (renders as black)
If you disable instanced stereo rendering, debug rendering renders correctly.
This was initially broken in 4.16 (and remained so in 4.16.1 and 4.16.2). Worked correctly in 4.15.
The bug UE-44947 is the same issue, however it says the issue is extra sphere collision being show and is associated with the VR template. The actual issue is all debug rendering being rendered twice, once correct, once black and distorted, when instanced stereo is enabled. The VR template provides simple reproduction steps, however the problem is not limited to collision geometry.