"The file could not be found" when working between Lightroom + Photoshop

When working in Lightroom, I often export to do "fine tune editing" to Photoshop. I make the edits I need to, then hit "Save" to send it back into Lightroom. When I do this, it creates a TIFF file. 

For years this has been flawless, and now suddenly when I hit Save in Photoshop... I go back to Lightroom and it says:
"The file could not be found." and it's missing.

Sometimes it eventually shows up. Other times, when I've been desperate... I've gone to through Finder to find the tiff file and manually imported it into Lightroom, but I obviously don't want to do that. Have I somehow unlinked the photo location or something? This has happened many times now, in many catalogues.

iMac desktop, masOS Catalina

Working off of WD 2TB Passport

All Adobe system are up to date