I’m getting the error 'Unable to parse move ‘G1 Z’. Also notice the print head steams off to back right position when no instructions was given to perform this action. I only try to extrude (load filament). Could this be the USB connection I have from the EBB42?
The issue is that variable_parameter_z define a gcode state variable named parameter_z, not z. Because z is undefined, G1 Z{z} is rendered as G1 Z which is invalid gcode.
I have no idea why these variable_parameters spread on github, this was never a thing. There once was a default_parameter_* (which is now deprecated and removed) where default_parameter_z defined a default value for the parameter z.
variable_ has a different purpose: it define a variable whose value can be modified with SET_GCODE_VARIABLE. If you only need a fix default parameter, delete these variable_ lines and use the G1 Z{ params.Z|default(20) } syntax.
For your issue of spurious moves, they cannot originate from connection problems, it is most likely a configuration issue.
Tried overwriting G1 Z{Z} to G1 Z{ params.Z|default(20) } gone unable-to-parse-move-g1-z but head goes back waits and moves to x0 y0 and stops. Resume required.