Final Cut Pro X 10.4 Not Seeing P2 Card Contents - Can't Import

This post piggybacks on an ancient thread on the same topic, so we'll see what happens. I have two identical Mac Pro's with identical OS's and FCPX installs. One "sees" P2 cards, one does not. Specs:

Mac Pro (mid-2012)

MacOS Sierra 10.12.6

2 X Intel Core 2 6, 3.46 GHz

32 GB RAM

Panasonic AJ-PCD20 5-slot P2 Card Reader

With both machines being perfectly matched, I've been able to swap boot drives and prove that it's not a hardware issue: the boot drive that can work with P2 cards does so on both Macs, while the one that's non-P2 compatible doesn't. So it has to be software, right? Both Macs are running identical FCPX 10.4 installs and I installed Apple's Pro Video Formats on both (ensuring compatibility with the P2's MXF files). I've trashed FCPX prefs and caches on the "bad" Mac to allow them to rebuild from scratch. I've copied-and-pasted same from the "good" Mac. I even copied-and-pasted the entire FCPX install (in the Applications folder) from the good machine. Still nothing.

The action I get when trying to import P2 material into FCPX is this: I hit Import, navigate to the P2 card (which does correctly mount as an external drive on the Desktop), and FCPX sees the contents for perhaps 1 second. Then those contents disappear and I'm left with a nothing to Import. The Import window remains open but there's no viewable contents. iMovie "sees" the P2 card's contents but claims it can't import them.

Transferring the entire P2 card contents (including the .txt file structure instruction) onto a different drive yields the same result: the "good" Mac's FCPX can Import, while the "bad" Mac's can't.

Any ideas? There's gotta be a software bit or piece that's working on one but not thing other, but I sure can't figure out what or where that is.