Upgraded Lightroom and lost PART of a catalogue (housed on portable SSD)

I upgraded to 13.3 to get the benefit of the new AI healing brush tools. My workflow for the past 8 months has been to import / open files directly from a portable SSD drive as my hard drive is getting full and I need to keep enough space for OS and Photoshop to work. When I launched LR, everything pre-update is there (small stuff for the past few months I used the hard drive) but all of my big projects are gone from the catalogue. They are not even listed as missing with a ?. They don't show as to ever been there in the first place. Obviously I have the raw files and some edits, but can I get part of a catalogue back? Has anyone every heard of such a thing?