Sounds to me like the bearing had frozen and had started spinning on the shaft. Like the others said.
I have had this happen several times since I spend a lot of time in the water. I can usually feel it when it happens if I am on the highway.
It feels like a tar strip or something that causes your truck to suddenly veer to one side just for a second.
That is when the bearing welds to the race. At that point, either the race starts spinning in the hub, which is really bad because it almost always ruins the hub really quick, or the bearing starts spinning on the spindle.
That is not quite as bad at first, because the metal is heavier, and will survive longer than the hub will.
However once you groove the spindle, its toast too.
When it happens, I usually take a grinder and grind whats left of the bearing down to the spindle, carefully, and split it with a chisel.
Or use a Dremal tool to cut a slot through it down to the spindle.
If you are really lucky, when you get to the point where it welded, you will have a small chunk of bearing sticking up on the spindle. You can then grind it down smooth, and everything will be fine. If you are not lucky, then part of the spindle will come off with the bearing.
Either way, whatever you do, DO NOT try to replace that hub until you have dressed up the sealing surface edge. I see lots of burrs and rough places on the edge just past your arrow. If you try to slide a new seal over that, it will be cut to ribbons.
I like a nice smooth edge with a tiny chamfer to help the seal slide on.
J.
