This is the problem of delay in changing between lists of materials..
Hi,
Go to viewports configuration>display performance and decrease baked procedural maps resolution to something like 1024 px or lower, see if that helps.
Thanks, but that didn't help anything
But I have an observation
This problem is old and was slower than that in the previous version Corona Render 9
It has been improved in the new version of Corona Render 10
Things have become much better than before, but the issue of slowness is still noticeable, and I hope there is a solution to this problem