Calibration issue - nozzle making contact with heat bed screws during Z axis calibration?  

Calibration issue - nozzle making contact with heat bed screws during Z axis calibration?

I finally got my new (secondhand) Prusa Mini+ up and running but it seems to have an issue calibrating. 

• During the last part of calibration, the nozzle makes contact with the upward facing screws in the heatbed.

• When printing the below print (without live-adjusting Z), the last two tabs are printing much worse than the others - I'm hoping this is because of the nozzle hitting the screws and causing an inaccuracy during the mesh bed levelling process - otherwise there may be another issue 😥 

Video

Whatever I set the z axis to, it always seemed to print 'lower' on the last two tabs and now I'm concerned that this may affect my actual prints e.g. the section of the print on that side may not be level with the rest of the print.

The printer was sold as Used but working as intended (i.e. no known issues). These are its upgrades, courtesy of the previous owner:

• Wi-fi interface

• 2 x new print beds

• Full set of new misumi bearings

• Bond-tech IFS extruder (internal filament sensor)

• Slice engineering copperhead hot end

• E3D 0.4mm nozzle x

• Original spool holder

• Squash ball feet

• Front USB screen

• Superpinda auto bed levelling

I've never had these calibration issues with my other Mini+ which is stock with no upgrades.