You're both right! The vertical bearings and the Z-axis screw were misaligned, and the plastic flange of filament spool holder was obstructing the motion of the bed. Unfortunately, my unit was shipped without empty lemonade cartons, but luckily for me, I hadn't removed my recyclables in days (another vote for procrastination).
First 'successful' test prints!
[left to right] Hal V, Air Chief Marshal Hugh Dowding