Zebra 170 Xi4 printer skipping in the middle of printing. Printer makes a slight jerking motion when this happens.

[Labeltech]

Sorry, I posted this in "Everything Else" since I didn't see a category for thermal printers.
The problem:
The printer makes a slight jerking motion while printing, causing it to skip on the output.
The printouts appear "crushed" across the label horizontally, about 1mm in vertical length. There is no gap when it skips which makes the printout come out looking crushed.
The jerking motion seems to happen consistently.
Doing a full calibration/loading defaults/cleaning doesn't fix this issue.

 

[Labeltech]

Some more information:
I visually inspected the drive belts but did not see any signs of damage (cracks, missing teeth, etc).
Belts appear to be properly aligned and do not feel loose.
The upper belt system seems to be the one causing the jerking motion. (Leftside schematic of the attached image)
It occurs about every 4 seconds.