I can’t chime in much help, only that i am seeing the same problem with 3 beta 4.

If i only have a few of the rom folders populated it seems to work fine, but when i add more roms to other folders i get the white screen issue, I haven’t yet been able to narrow it down to how many, but i will try your 20 or so folders and see it that makes a difference, along with the renaming.

I have struggled to find this issue with a solution anywhere yet, but will keep looking.