Have you got this issue sorted?
Is it slow because the board is doing full memory checks at startup, or other high end server board things?
Have you tried disabling certain features in the bios?
I am curious, because I plan on a very similar build and wondered about the memory myself, as posted here:
https://forum.level1techs.com/t/question-any-compatibility-issues-with-this-nemix-memory-for-threadripper-pro/
I see you haven’t gotten any responses here but I’m very curious to know if you’ve resolved your issue.