Depth is off inconsistently during carve! HELP!

I am using my x-carve to cut and engrave christmas ornaments on 1/4 inch plywood. The engraving depth is set to .03221 for everything. I have made a dozen of these with no problem but now this keeps happening!? It INCONSISTENTLY engraves too shallow. It also show the “staircase” cut in some areas?

Ive done all the preliminary checks, nothing is loose or needs to be tightened, the plywood is not bowed and is anchored secourely to the washboard, and the bit is nice and tight in the collet…suggestions!!!

you can see in the picture directly above that, I stopped the carve after ONE pass at the circle. You can see it cut much shallower at the start of the circle then went counterclockwise and at the end cut much deeper

Xcontroller or gshield?
What is your GRBL value $1= like? (should be set to 255)