Jittering, fps jumps (HTC VIVE + big scene with light/shadows)

Hi there,

with the latest editor releases (~5.6, last 1-2 months) I'm experiencing an issue.
I have a big scene (over 1M polygons), 2 months ago everything was fine, but with the latest official releases I have FPS "jumps" like from 50 to 90 fps. Looks like evrything is jittering on the scene (including visual controllers).
If I have 1 direction light with shadows enabled - I have this fps range 50-90 fps,
If I turn off shadows for the light - FPS is stable 89-90 and everything is...

Jittering, fps jumps (HTC VIVE + big scene with light/shadows)