Odd shimmering artifact on foliage - any ideas?

Any idea what causes this strange shimmering light artifact on meshes in the scene. It’s more obvious in the distance but still happens close by. I’ve tinkered with all sorts of settings, UE versions and scalability options. I’ve tried changing meshes, removing textures and uvs, adding/removing post processing, switching off/on shadows, disabling lumen, GPU antialiasing .. you name it. It’s not evident in unlit mode, so likely related to lighting.

All suggestions welcome. Thank you.

i really can’t distinguish what’s on that scene.

i wonder if this is yet another case of moire effect.