Okay, so start over, with just a single CF Card: use the smaller one, 64GB, in the "master" slot of the dual adapter. See if you can get that working first.

EDIT: Once that is working, and the setup again proved to be sane, then try two cards, noting that the builder will REFORMAT _both_ cards.

I don't have any 128GB CF Cards on hand, so I have never tested with those. If either of the Sandisk cards you have claim to be "CFast" or "CF+" rather than plain "CF", then that would explain the issues.