Issue with dimensional accuracy on the z axis

I have a model that is 171.45 mm tall, I printed it out of NylonX and after measuring it came out to 167.85 mm.

I'm trying to understand, what could cause this?

I'm not sure I've ever had dimensional issues on the z axis. I did recently switch to RatOS v2.1.0-RC2 on my V-Core 3.1 400; I can't imagine that is the issue. Open to ideas.