Back at the table I have narrowed it down and it appears the activation of an actuator just next to to the Phidgets motor induces a very short communication break. The closer the two are, the worse. It even happens when the actuator is powered from a different source with no physical connection of the circuits. Some electromagnetic effects must be at work.
All 3 autosteer kits I built have this same behavior so I’m thinking the central units are built and soldered just fine. Either the central unit has some undiscovered weakness or else this particular setup with actuator-motor is the coincidental problem causer. Which I find strange because I was using it for 3 years in a setup with everything connected with bluetooth modules (HC-05).
Someone who recognizes this behavior or might know what to do/try? My next field test will be without actuators for sure. Which is a bummer, it was a quick and easy way to disengage the steering motor.