Multicam 7000 Series Homing Issue

We have a Multicam 7000 Series CNC Router and we are experiencing "X Homing Failed" issue. We have replaced both the Xa and Xb motors and the associated gearboxes. However, the machine does not home correctly and there is a calibration error also. We have tried homing by loosening the gantry screws as advised by the engineer. However, the issue does not seem to solve.

We are a signage firm so we cut all sorts of materials with the CNC router. I would really appreciate your help on this matter.

Thank you