Shader .... unknown by landscape thumbnail material, please add to either...

Hi,

I already posted a question about this issue in the AnswerHub a bit over a month ago, but, as I still hasn’t found a solution I thought about trying my luck here as well.

In summary, I get the the warning message below about 8000 times, and I need to get rid of the warnings, soon, but I have no idea what is causing them to pop up.

Shader … unknown by landscape thumbnail material, please add to either AllowedShaderTypes or ExcludedShaderTypes

You can take a look at the oriignal question in the link below

I would appreciate any help or advice regarding this issue.

Thank you.