Hello,
I’ve just encountered the same issue with FTP restores (on versions 1.683 and 1.682):
In DirectAdmin, I go to Admin Backups → Restore, switch to FTP, and for recent versions, the "Next Step" button stays disabled. If I click "Reload Files", then "Next Step" (2x), the page goes blank when attempting to display the files.
I haven’t tried disabling CSF yet, but I believe it should work with it enabled (as it always has).
P.S. I also discovered the same issue occurs when using the Local restore option.