Dirty z axis which is binding, or exactly what the warning says are the most likely causes.
A couple years late but was using forum to troubleshoot. I started having problems coulnt figure it out so I attacked z axis. WD40 air wipe down = still acting up. Took off torchand REALLY cleaned it now it cuts like butter. What I learned althoug it looks clean it thrashed with stuff you cant see and needs to be cleaned cleaned.
Thanks