Prusa MK3S - Persistent "Calibration Failed! Check axes and run again"  

Prusa MK3S - Persistent "Calibration Failed! Check axes and run again"

I manage a public library MakerSpace with 5 Prusa printers, two MK3S, one MK2, and two MINIs, and I handle repairs and troubleshooting for all printers.

I've been having an issue with one of the MK3S's, where every so often, it would crash into the bed.  I'd run XYZ, no issues, and it wouldn't happen again.  Last week, it happened 3 times in a row, so I took the printer out for maintenance.  I ran XYZ, and it threw a "Calibration Failed!  Check axes and run again" error.  I inspected the Z axis, made sure everything was lined up and moved properly, made sure that the trapezoidal nuts at the motors weren't impeding them, same error.  I made sure that the PINDA was working and communicating with the Einsy, it works fine.  I adjusted the PINDA up and down with no luck, and I noticed the error pops at the exact moment the PINDA triggers.  I've been at this troubleshooting for 3 hours with no luck - It does mesh bed leveling just fine, it auto-homes, but as soon as it goes to print the nozzle crashes into the bed, and it won't let me calibrate Z.  I've got over 2000 print hours on this MK3, and I've not had an issue like this.

Here's everything that I've tried today, per other posts in forums:
-Lubricating the Z-axis smooth rods
-Re-running the pre-flight checklist
-Switching to a fresh nozzle and re-aligning the PINDA
-Manually topping out Z before starting calibration
-Checking that my hotend was installed at the correct height (against the other MK3S)
-Re-flashing firmware (3.10.0)
-Running the Wizard
-Live-adjusting Z prior to calibrating

For some reason, it's expecting a Z-axis length that it's not observing, so my next steps are to factory reset and flash fresh firmware, then fully disassemble and reassemble, which I'd really like to avoid.  Thanks in advance, folks, let me know if any additional info or images would be helpful.  I'm really hoping it's something minor I missed.