I read your post just today while searching for another topic, and thought I’d chime in as well, just in case something may help your issue.
We’ve recently serviced an UP BOX+ that ad this very issue (request for Auto Calibration results in no servo flipping down, and printer just moves to the 9 points, but no measurements are taken). In this case, the servo was newly replaced already, and the small ribbon cable running to the servo was also tested as working.
My next assumption was the wider, white FFC ribbon cable from the back of the printer to the toolhead (Since this is a consumable part that does often get replaced in the UP BOX+ printers that get frequent use). Upon testing with a different FFC cable, we found that the FFC converter (the small PCB at the back of the extruder) was the actual culprit.
Whether you’ve ever swapped out the FFC cable in he past or not, the connector on the FFC converter board where the FFC cable connects, can become an issue over time. These FFC cables can get a fatigue spot, usually along the edge of the extruder, when the extruder is extending and bending the FFC cable the most (when in the front left position of the print bed). After some time, the FFC cable can begin to faulter. If the FFC cable isn’t your issue as you had stated from your testing (keeping in mind a single trace within the FFC cable could be bad, leaving the other traces intact) then I would certainly consider the FFC converter board. All of your data that controls the Z auto calibration probe goes through this FFC converter board, the FFC cable and the small Z probe ribbon cable.
I hope this information is in some way helpful in your resolution.