Scene capture latency in VR


I have setup an extra camera pass in VR using scene captures. It works by getting HMD projection matrix for each eye, setting those as custom in scene capture and compositing the extra render textures in a post process material.
The implementation is close to…nreal-engine-4 but all is done in blueprint, except getting the HMD proj. matrix, which is done using a custom pawn class.

Problem is : renders are in place but when the framerate is a bit low, the extra pass jitter. Either it is one frame late, or the VR reprojection won’t work, or both…
This guy…effects-in-ue4 made a very similar setup and he mentioned solving it :

Unfortunately the thread is old and the link is broken.

Any idea ? Thank you !

(I’m using Oculus Rift. I’m posting in Rendering because if it is just a matter of a one frame delay, it is not a VR specific issue.)

Edit : After some more testing I believe this is related to the asynchronous spacewarp or some reprojection technique that is not processing over the rendertexture, since the full screen rendertexture alone is jittery on low fps.

any news on this?