Yeah, hard to diagnose with all that’s going on in those prints. The layers appear stacked fairly consistently vertically, but they look somehow wavy, and its hard to tell exact in which axes. Also, the corners look to have some serious over extrusion issues. Have you ruled out extruder and temp issues as the cause?
The fact that the layer lines appear consistent doesn’t make it appear mechanical in nature, but its really hard to say based on a rectangle. maybe your steppers are somehow intermittently missing a step because the driver is failing, wires have frayed and are introducing additional resistance, or the bearings aren’t running smoothly.
I would print some calibration cubes one at a time and verify how consistent the z axis error is. If it’s identical cube to cube, it’s likely a settings issue. Reflash firmware and recheck slicer settings. If z height varies cube to cube, it’s likely something mechanical or electrical is causing aperiodic missed steps.