Recently, the new terrain UI had been giving me problems with heightmaps, you cannot remove an image that served as a heightmap, image below.
When you click that button, above shown it does not remove the heightmap image.
I have already attempted to solve the problem by using different accounts, computers, and IP’s but nothing appears to change the outcome. Although the older Terrain UI does work it has limitting factors to heightmaps, and yes this was previously working for me. This may be a bug but I’m not sure as my 1 of my friends are experiencing this issue.