Android VR (Oculus Quest):
On moving from UE4.20 to UE4.21 with the RHI thread enabled, we are no longer running at a consistent 72 fps.
Looking at a profile capture, it seems to be because when we go to render instanced mesh particles, the render thread stalls allocating a vertex buffer (can be 10+ms). Tracking back a frame it appears that the RHI thread takes a long time to present (6ms in FinishRendering).
I tried disabling the RHI thread but perf suffered even more.
I can supply a ue4stats file if needed.