I was doing some tests with progressive caustic and the results were great but out of the blue I was getting this error in rendered image. What is weird I got the same results when I switch to photons. Opening fresh max with this scene gives me the same results, camera or perspective view same results.
3dsmax 2019 (tested with 2022 too) and the latest vray build.
It just looks like the sun photon radius is set too small.
Playing around with this value does not make it better as there is no caustic at all (for photon map calculation). Anyway I have attached the scene.
Caustic.zip (49.6 KB)
Your scene file works as expected if you increase the photon emit radius to capture the water, as Sirio mentioned.
Scene reattached with that set 
Caustic.rar (46.8 KB)
It is not the search value, you need to rise the sun photon radius so that it can contain the pool dimension. Look at this tutorial at 3’20’’ https://www.youtube.com/watch?v=ol4ebKsUdz8
I recorded the video in Vray for Cinema4D but is the same in Max.
Thanks, that helps:)
This is also valid for the dome light, if you have one in the scene.