Hi,
We have greatly improved the 2.5d displacement tessellation in the latest v7 daily build.
It should remove a great deal of the artifacts which were caused by the 2.5d displacement. You can find a build here: https://forum.corona-renderer.com/ Corona Renderer 7 for 3ds Max - Daily Builds Changelog #msg182287
I will look forward to your feedback.
Cheers,
Rowan