So far it seems to be rendering ok here. Some questions though:
- You have multiple LightMix layers set up. There is no support for multiple LightMix layers at this time, what happens if you delete those extras and just have the one LightMix?
- I am not sure what your sample renders show in the first post - are they Beauty passes, LigthMix results? What's the difference between the first and second image, since one has those strange patterns on it, and another does not?
- No textures included with the uploaded file, not sure if that makes any difference (could be no textures are used)
- The Render Settings show the Ambient Occlusion and Global Illumination options present and enabled, but Corona doesn't use those. What happens if you delete them?
- Caustics and Sketch and Toon are included there too but not enabled - all the same, I would delete them since they are not compatible with Corona and who knows what odd effects they could be causing (worth a test to remove them!)
- Was this final render, or IR? If IR, what happens if you disabled Fast Preview Denoising?
I only had a few fireflies on some metal objects (the railings) in the "sun" LightSelect layer only.