Figured it out - I didn't realize that the path in Home Assistant changed - it should be the serial path instead of the "by-id" path. This link helped me figure that out (specifically point 8 in the post): https://community.home-assistant.io/t/solved-conbee-2-fails-to-connect-to-zha-ha-in-unraid-vm/431276/2
Strange.. just tried an upgrade to 6.10.3 from 6.9.2, and still broken for me - I must be doing something wrong or my NUC has some special features that are messing with the USB bus.
Just adding on - this was the only thing that worked for me. As soon as I rolled back, everything worked flawlessly. Looks like a regression with 6.10.x.