I recently acquired a CR-10 v3 and was having some issues with prints lifting at the edges which is something I did not have on my Ender 3. I set bed temp to 70c and let it heat for a while to equalize. Actual temps on the glass range from about 65c in the center to as low as 57c near the edges. Is this a calibration issue or a failure of the heat mat? Has anyone had a similar issue?