I installed MAMEUIFX 64 bit today, .171.
I pointed it at my ROMS folder, but it only displayed 38 titles in AVAILABLE, with the rest (10,000+) as UNAVAILABLE.
I ran an audit on all games, but nothing in the interface changed. If I started a game from the UNAVAILABLE folder, it worked.
To cut a long story short - to fix it I had to enable ENABLE SCAN OF 7-ZIP archives, which was OFF by default.
It was a bit puzzling at first. Don't know if this is useful at all........