Flickering or shifted color will be seen in the Right Eye. User reports that moving the nodes from the material function to the base graph resolves the issue.
Confirmed in 4.23 MAIN branch @ CL 6395234
4.21 Sample project attached (Verify in 4.21 and update to 4.22)
With instanced stereo on - Play in VR Preview (also seen in packaged project)
Result: Particle in right eye will flicker or be a slightly different color
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-74539 in the post.