I work with Rob at Techgage, the author of the article that highlighted the issue with the Interior render. KeyShot may have figured out the issue already with the 2990WX, but I am here to make people aware of some of the extra testing we did on the CPU:
https://techgage.com/article/threadripper-2990wx-performance-coreprio/The short of it is that Windows' thread scheduler is not optimized currently, causing issues with cores without direct memory access. AMD Dynamic Local Mode tool does not solve this issue for KeyShot, however a third-party tool called CorePrio does help in some cases. When enabled, it nearly doubles performance - after a few attempts. When doing the render passes, CorePrio did not work on the first attempt, but on subsequent attempts, it did resolve the performance regression.

When we tested applications under Linux, we saw little in the way of regression, so it's definitely a Windows related issue for the most part.