Cutting Depths

Hi all. Not sure which way I need to go as the two problems seem to contradict one another.
I tried to cut out 4 X 120mm circles from 3mm MDF, material running left to right, and it cut the first circle out (the one on the LHS), then progressively seemed to raise the cutting depth, thus the other 3 circles didn’t cut out.
On my second job, 19mm pine, similar length, cutting a 4mm pocket, the left hand side cut to 4mm deep, but the depth got progressivly deeper, to 7mm, on the far RHS.
My board is surfaced and level, as is the machine. I would have thought that, if anything, the pine would have cut shallower to mirror what it did on the MDF.
I’m using easel and a 1000mm x carve. Any ideas?? Things to check??
Thanks Phill

Double check the tightness of the cutting bit. I forgot to tighten the collet nut on a project, and the bit moved up and down in the program. I caught on as the program ran and stopped the program before the collet nut came completely off the spindle.

Check the tightness of the set screw on the z axis pulleys, both on the motor and on the acme screw. If these are loose you will get results like you describe.

If you are just measuring the depth of the pocket and they are varying the other thing you might check is if the material is a consistent thickness on both ends.