Can't speak as to your specific issue, but I've come crashing down in a similar manner with no toggle failure though.
The whoopie had slipped off the knot (and evidently enough off the toggle) that when I sat down, boom. This was after I was fiddling with tightening and loosening the whoopie a few times.
I ended up flipping the whoopie the other way around with the fixed eye at the toggle and the adjustable eye attached to the hammock with a Dutch biner and chainlink girth hitched to the hammock.
So from the tree - MSH with toggle, fixed eye of the whoopie, whoopie sling, adjustable eye of the whoopie, Dutch biner, chainlink.
With this setup, anytime you adjust the whoopie sling, nothing moves at the toggle. So, once you put that eye on the knot on the toggle, it doesn't move around at all - no matter how much you adjust the whoopie.