Forgot to say that I tried everything we mentioned here, but the only result I got was that there were not so many black spots as before. Ended up fixing that in PS
Hi, disabling caustics adaptivity in the devel/experimental rollout should fix any "dark/black squares" visible in caustics.
If it didn't, or if you are having some further problems, please contact us here and attach your scene if possible:
https://support.chaos.com/hc/en-us/requests/newEven if we will not be able to help you (sure it does sometimes happen!), we will have a scene where we can reproduce the issue and this is extremely valuable for Corona development. We can pass it to our devs and they can do their magic.
The scene could be either your original scene (if you can share it), or a simplified version of it (if you can create it), or our own, but the most important part is to reproduce the issue.