It appears that there is a major bug in Mach4 + ESS combination, which we can not address in the PoKeys plugin.
Eventhough PoKeys plugin instructs Mach4 to jog, the core should not do anything if it is disabled. Moreover, ESS device should not produce any motion if core is disabled.
We don't know how your hardware is configured, but I would start by checking your matrix keyboard for proper functionality (use PoKeys application to test it to be sure it is operating correctly). We will redo some tests here, but as I pointed out, this issue is related to the Mach4 and ESS plugin in how these two operate and talk to each other in 'Disabled' state.