Water4 error flushing culler

I have this error with my water:

Flushing Culler but we havent completed rendering. Are you setting material.shader inside of a Render call?

I simply replaced the tile its mesh with my own mesh as mentioned in this blog.
(hard to find any documentation on unity water 4 …)

My mesh has holes in it (because some parts of my land are below the water level so I needed a hole in it.)

This seems to have fixed itself after restarting Unity.