Media Management Transcode Used Media doesn't work any more?

Subject says it all, really.

I have a bunch of mixed res/framerate/codec/wrapper material that I need to transcode to Prores.

Some of the source clips are 30mins long, and I'm using 10 seconds of it, so I want to take just the used media, perhaps with some handles if I'm feeling particularly saucy.

When I have Transcode All media selected in the Media Management Settings tab, it happily says the current size is xKB, the New Size will be xxxKB.

But when I click either of the Used Media options, both Size figures go to 0KB and don't ever update, even if I select just a handful of files.

I have done this in the past without a problem, on the same hardware, using Resolve 16.

Ignore my sig specs. This system is a Hackintosh (shh!) running Resolve Studio 17.2.1 Build 12, under macOS Mojave 10.14.6. i6700K 4 core 4.2GHz, 32GB DDR4 RAM, AMD Radeon VII GPU, a whole messa Thunderbolt storage.

Thanks for your insights!

---=== BREAKING NEWS! ===---

I've just bounced everything over to my primary Windows machine and it's doing it there, too.