Good safety tip Mike. Sounds like that chain was either overloaded or over stressed from prior loads.
At our levels of stress (around a 1000 lbs) most good size chains like the one pictured, wont rebound much, if any. I have my chain pop off items regularly under heavy tension and it hardly moves at all. Mr K. can only impart so much yank or pull. At 36,000 lbs, anything can happen....
I've been researching working and fail limits on chain, rope, and synthetic because my faith isn't strong enough to tell my remaining dogwood to get up and go into the sea, and the efforts I've been able to make have only bent it. I learned an interesting fact about chain that in retrospect should be obvious: when chain is stretched, it doesn't spring back to its original condition; in fact, its reduction is only a tiny amount.
The federal requirements for chain is that it stretch at least 15% before failing. So your new 40' logging chain, stretched beyond its limit, will have stretched to 46' -- all of which is under tension, and the failure will cause the chain to whip back those six feet.
Funny thing (to me), though: if the chain is overloaded only, say, 7% beyond it's limit, then next time it's overloaded and breaks, it will have only 8% (well, minimum, but manufacturers aren't going to build in 25% margin, or even 18%, or any more than they must to ensure the 15%, eh?) -- so let's say 8%, which means that it will only snap back three feet or a bit.
This means that those times that chain broke from an overload and didn't seem to snap back, it must have already had all it's "stretch" stretched out of it.
None of which is getting that dogwood out of the ground.