Lightroom Classic Export Error

I'm using Lightroom Classic 11.5 with desktop running MacOS Catalina 10.15.7 and suddenly cannot export files edited in LR after uploading to my external drive from a CF card (Mamiya / PhaseOne .iiq). "Unknown error" message when attempting to export to jpg (on desktop or external drive) or even to Photoshop. I have gone into Mac preferences and given full disk access to both LR and PS, as well as resetting LR export preferences to default, but the same "unknown error" message comes up. Also tried upgrading a laptop to MacOS Monterey and updating LR, but getting the same error. Not having the same issue with images uploaded from SD card and different camera on the same shoot. Any ideas?