I was wondering if there has been a workaround develloped for this problem (black sun / weird reflections). I refer to below post and the problems:
Is there perhaps a special “corona backplate material” available? I know how to work around this problem, but (as far as I can see) it just isn’t really a nice solution.
Unfortunately, we don’t have any fixes so far. The solution is to either restrain from using such setup (e.g. using environment overrides instead of backplates) or using the known workarounds such as https://forum.corona-renderer.com/geosphere as background#msg181607