Project Manager broken? It fails with "An unknown error occurred during the Project Manager operation."

Hi all.

I'm trying to use the Project Manager as I normally do when I'm mostly done with an edit: "Collect files and copy to new location" for color correction and audio post, excluding unused clips. Those are the only checked settings in the dialog.

On my latest project, this fails less than a second after it starts "analyzing project." It worked fine on a different project yesterday. The one it's failing on probably has a less-complicated structure; it's pretty simple.

Anybody have insights on this, or workarounds?

This is Premiere Pro 12.1.2 on Mac OS 10.13.6.

Thanks!