Today I removed my snow tires and mounted my all season tires on the 17" alloys.
I always hand tighten the lug nuts, snug them down with a breaker bar then use a torque wrench for the final tightening.

When I tried to tighten one of the lug nuts it started to get tight then it just spun and would not tighten.
When I tried to loosen it the lug nut started to tighten again then spun off.
I checked the threads in the lug nut and the threads on the post and they seemed fine.
I even tried a different lug nut and had the same result. Unfortunately, due to lack of time I was not able to diagnose
the problem any further or actually confirm the post was spinning.

Has anyone ever had this happen to them before?
Do posts just spin once the lug nut started to get tight?
Tried the search feature but could not find anything.

Any thoughts would be appreciated.

Sounds like the stud is not seated properly and is turning where it should be seated.

take the wheel off and put a lug nut on the problem stud and tighten it till its snug and see if it spins in the hub. if so, it may need to be re-seated or replaced.