Spicer hubs

[6869704X4]

I’m on the highway doing 75mph when I feel the truck jerk slightly to the left and hear a metallic squeal. This lasts for a fraction of a second. Then everything feels normal. I pull over at the next exit and check things out. Don’t find any thing so off I go. Ten hours later I go to lock the hubs and the left one wont budge. I pull the hub apart and find the inside of the locking knob was melted and had been slung outward. This allowed the hubs to try to engage.
What I can’t figure out is what got the hub so hot that the knob melted. I first thought the brake was dragging but they checked out OK. If the two locking pieces were spinning against each other that would create heat. But how would they get together? The selector was still in the free position.
What really sucks is I had to buy a set of Warn hubs. It was too cold to change both so I had one Warn and one Spicer hub.
Anybody have any experiences with Spicer hubs trying to engage themselves?