When I used the new water system for 4.26 in a large (8km by 8km) landscape The water plane will not render (but the underwater postprocess is fine). I did a controlled test to verify and get some info on the problem.
I built 2 new projects, 3rd person example: then I
- enabled water and shallow water
- imported a landscape (shown is the settings for the 8km landscape, the only change for the small landscape is that I reduced the number of components to 1x1 and the section size to 127 so the total res was 256x256
- restart editor
- placed a lake
here are the results for the small and then large landscape
I didn’t test to see whether it was the size or the resolution of the landscape that was the problem. If that’s relevant I can definitely test.