Grass 'flashing' in EXR Path Trace render + in Lumen too

Hello!

I am trying to render out a short camera sequence for a project, and have tried both Path Tracing and Lumen but seem to be getting the same issue every time. Everything else in the scene renders fine, the quality is all good but the painted grass i have on the ground changes colour with every frame, flickering back and forth? I will attach an example video if possible - not sure if this is a lighting issue or something else? I have two-sided textures on for the grass but it doesn’t seem to help the issue. Any help would be massively appreciated, thanks!