Hi dkoneill,
thanks for your trust in my testing abilities 
The step should be from v1.17.1 to v1.20 as recommended here.
Do v1.17 → v1.17.1 first (if not done already).
My SD card was never used as adoptable storage so that was not an issue for me. Check status of your SD as suggested by @aibd
IF your SD-card is adoptable storage I cannot say what´s best to be done.
Maybe it is possible (should be I´d expect) to undo this specific SD-card-integration into internal storage in system settings before upgrade (?)