I'm getting a black surface.
I'm getting no errors.
I'll look into the things you suggested, thanks for your input!
EDIT: I also tried rendering with Superpower's renderer (in gameInstance.threeRenderer) and that didn't work either. I didn't edit the time uniform, that could be the problem.
EDIT 2: trying to set the map of a MeshBasicMaterial doesn't work. Type script won't let me set a texture property to a WebGLRenderTarget.
EDIT 3: I got it! I was forgetting to do a normal render after rendering to the target. I thought it wasn't needed.
Thanks for your time and help :)