SimpleHMD rendering issue

Hello all,

I have an issue with SimpleHMD plugin under UE 4.20 and 4.21 (might be lower versions as well).

Only one eye is properly rendered, the other one seems to have a shader problem.

I did not have this problem under UE 4.14.

Here is a picture demonstrating the problem.

Would anyone have an advice ? What should I tey in order to fix it ? Any clue would be welcome !