Aspire design, gcode sent through easel

I designed a plaque Aspire, and then am carving it out through easel. I have done a rough cut for the letter, finish on the letter, then a rough for the relief or whatever (3d in aspire). Everything looked great until i started the finishing paths. It looks like (only 2 so far) every inch or so it carves a few lines deeper? Any ideas on what I should check? You can see the line right below the text, and about a inch lower again.

Your Z axis is slipping check pulleys , set screws make sure bit is tight in the collet.

thank you, I will check it when I am done. It seemed odd it was doing it in actual increments…but the rest of the carve it wasn’t in increments.