Why am I getting Z banding/shifted layer on a single layer?
I started this as a comment but it couldn't fit.  If it isn't a true answer and should be removed, I understand.

You suggest in your question that perhaps the defect could be caused by a problem in the Z-axis lead screw.  Indeed, that is possible.  If so, it would probably introduce a defect at that position across the entire print bed.  If you print a test object and the defect is on all faces at the same height, check your Z-axis.  With the power removed, try slowly moving the bed up and down through the region where the defect occurs, feeling for any hangup, hesitation, looseness, or any other non-uniformity.

If the defect is along a particular line, check the complementary axis.  If the glitch is a X-axis line, check the Y-axis.  If a Y-axis line, check the X-axis.  Slid the axis back a forth slowly, feeling for any non-uniformity in the motion.  It could be a scratch on the linear bearing, or a ding from dropping something.  Any discontinuity  can cause a linear Z-axis defect, up or down.

It could even be cause by the printer not being firmly sitting on the table at an angle, so that after a particular point the balance point changes and the printer rocks, introducing a glitch.

3D printers, and many other motion control systems, relay on flat, smooth, uniform bearing surfaces connected to smooth, continuous drive systems.

If you attach photos of all four surfaces, we might have a better idea of how to look for the problem.

It wouldn't hurt at this point to wipe and clean all sliding surfaces, and then re-lubricate them.