Z axis slippage - FIXED

If I print about 2 mm tiles, everything works fine. But if I print a figurine, say 50mm inches high, about half way through the print, the nozzle head is scraping the extruded plastic and simply making a mess. it’s like the software is not raising the extruder properly or consistently. The offset seems fine for thin projects, and the skirt looks smooth and even. Thoughts?

I’d make sure everything is tight (screws/belts) and square (gantry). I had some pretty bad issues when my belts were slipping

The problem eventually turned out to be non-manifold edges in STL files I purchased on CG Trader, which when I either deleted or fixed, solved the problem. Everything prints smooth and as expected.