Has anyone same problem ?
Okay. I may have found a fix for this. In my case where I was loading in terrains dynamically I needed to make sure they were not set to Static in the inspector. Not sure if that is the same problem you were having, but hopefully it helps someone.
I had the same problem with dynamically loaded terrains. Making terrain material to null worked for me. CPU cost of terrain reduced to about 1/3. I’ve sent a bug report.
I hope this helps someone.