It’s possible that the layout of the ballot makes it more likely for the votes to switch in a certain direction. Especially since it sounds like they are using resistive touch screens. If the Republican option was on top and the Democratic option was right beneath it and if people are more likely to hit towards the top of the option, a poorly calibrated touch screen could cause votes to swap (initially selecting the Democrat and then the screen gets confused depending on how the pressure changes as you take your finger off and then selects the Republican above it). These kinds of errors were fairly common when resistive touch screens were the norm.

Then the technician comes out, hits firmly in the middle of the field, sees no problems, and calls it a user error.

In Texas, they used a machine with a kind of joystick to select between the options. And those had a tendency of overshooting the center when you let go of it, so the selector would go back up as you were reaching to hit the next screen button. They put incumbents at the top, so it was more common for people to see it swap from Democrat to Republican than the other way around.

It shouldn’t be acceptable to run elections with machines that have these problems, but there’s no real incentive to fix it.