VFD spindle not stopping completely

Hi Running a Huanyang VFD and 2.2k matching spindle, System has run perfectly, When Mach3 sends a M5 command, spindle keeps turning fluctuating between 42 and 72 RPMs.
If I push stop button on VFD controller pad, then it stops completely, as soon as I push run on VFD Controller pad it restarts fluctuating.
Mach 3 controls speed-up speed-down perfectly.
I see no fault codes appearing on the VFD.
Any help or recommendations would be greatly appreciated.

Thank you

Onefinity does not use mach 3.