Hello Again,
Just a few points I hope you will find helpful.
If Mach3 locks up when starting the spindle just unplug USB to RS485 converter and Mach should recover, to test again close Mach 3 as normal and then plug USB in then restart Mack3.
Might be useful setting PD024 to 1 so you can switch Spindle Off via Stop Button on VFD.
Thanks,
BK.