Very slow to react when homing

[ReggiePye]

I just built a new laser machine,
This one has limits at both ends on the X and Y and a single limit on the +Z
When I press a limit switch by hand it works, but is very slow to display on LaserGRBL.
When trying to home the Z lifts up and triggers the limit but no reaction and the motor keeps running until it has locked up.
I have to disconnect power to release the motor and wind it down by hand,
I have checked my wiring and tested manually by hand triggering the limits, all work but VERY slow to register that they have been triggered.
Have I done something wrong? I am at a loss with this one.
Windows 11, GRBL 1.1h, CNC Sheild v3.00, Z limit on SpnEn, Spindle PWM on Z+ (works laser module OK)