Lulzbot Taz Pro - Z Axis Motor Sync / Carriage Alignment

Taz Pro (dual extruder) has developed an issue at start of a print. At the beginning of a print, the carriage moves to the the top of the frame (as if homing) and the left Z Axis, skips, jerks, bounces, etc. for a few seconds and then restarts the unit. In order to access the printer functions afterwards, I have to close the cura software and re-open and re-load a file. In case it is relevant, prior to printing, homing the axis functions as it should, but notice that the left side drops off of the contact switch quite a bit compared to the left.

I believe the sound is caused by the belt slipping under tension. I have tried adjusting belt tension, rod alignment, frame alignment and cannot determine what is the cause. I slowed down the acceleration and velocity to video what is happening because it was happening to fast to video in standard mode.
Below link should play the video.

Appreciate any input that will help resolve the issue.

I don’t think it is the belt slipping (you can check by marking the belt, see if the marks move relative to the pulleys), I think it is the stepper motor missing steps because it has hit something solid eg the top of the frame. I’d check that both those switches are working correctly, wiring not cracked or broken etc.

Thanks for the input Chipwidget.
Tech support was quick to get back to me. It ended up being the thermistor that caused the stuttering. I wouldn’t have expected it to be related, but it was the issue. I pulled one from an older, worn out head and got it running. Will need to add some spares.

The actual part below.