Could be 3 things.
Z axe wobble, yes it can produce this, if the alignment of the axe is off, or it is wobbly, chances are the movement is not smooth.
Best check with micrometer, do a movement of the bed in 0.1mm steps, end check the micrometer.
Could be filament. Check you filament in diameter on several places, also check the roundness.
And from what i hear, could be temperature deviation on the printbed. bed height is influenced by the temperature, so if there is a fluctuation, then he bed can expand or retract, give this result.
First get the Z axe fixed!!! Otherwise this problem will hunt you on every print :-(
I had the exact same thing! On the right side of the bed, you'll see an open side with 2 brass bushings. One or both of them might be loose. Apparently they forgot to add epoxy to lock them in. They have it on some.
I created a part out of ABS, about 8mm x 60mm tapering from .2mm to 2mm. It was overkill, but it worked. Wedged it in the gap in the front of the bushing and the side to side movement of the bed stopped.
To get it in there permanently, I made a tiny bit of ABS/Acetone slurry and dipped the tip of my shim in it. Then I wedged it in the gap. Left it to cure, maybe 2 hours, clipped off the extra bit and it's solid!