Mystery
You'll eventually figure out what it's deal is, and it will be one We'l all probably learn from.
The only thing I can think of, is that maybe there's a burr, or rough spot. You'll find it, if there is.
If there is, it probably inside the agitator.
( wouldn't be on the post, that would make it too easy ) LOL
I have never had this problem (hope I didn't just jinx myself) and to be honest, I don't lube the post very often!
Mine will float off, but only if its full of water, and no clothes.
So most of the time, it happens as I'm wringing clothes threw, and there is only of few items left, or completely empty.
I've always considered it a minor annoyance, especially after seeing what Larry went threw to get his off! After that I decided
" who cares, let it float "
You could try using a Bobbie pin with out the rubber thing on the end, a little WD40 and use it to clean the spins on the inside of the agitator. Maybe there a chunk of rust or something in there? Try getting into the sunlight where you can see down in there.
Let us know!
Stan