I experimented when I did broth last week - only the old lids failed on me (& just old, not re-used - I don't re-use them). The new ball sure tight lids all sealed. The old lids were given to me from a neighbor though so in reality they could have been years & years old. But I was happy all the new lids sealed.
I posted a video of that a couple years ago here - it was funny! The jar did seal fine in the end. I do believe I over filled my jars a bit that time, I make sure I no longer do that & I haven't had any siphoning since (no clue if that had anything to do with the popping tho). I was guessing on an inch headspace & I was wrong, lol. It was more like 3/4. Got that down now.
When water boils, it will expand 1580 times it's size. at a very minimum With those jars closed, it has to go somewhere, so it pops and fills the little void with the steam, hence you hear the lid popping up from the bit of pressure it created under them. If you look closely every time the lid pops up you seen a bubble run up to the surface immediately before that event. That steam then cools back down to water, immediately contracts, creating a vaccuum under the lid, and it sucks back down. Given the jar is right @t the boiling point, small amounts will flash in and out as residual heat enters from the pot it's in, and leaves due to the lid being off and natural cooling.
The thing here, every time it sucks in, it has a chance of sucking air in from the outside too, air that can have mold spores and everything else in it, hence giving it a perfect night cozy, place to grow. Leaving them in the pot, with the lid on, does not have to be sealed tight, but on, keeps the entire area surrounding it, hot, YES it takes longer to cool down but the entire surrounding is sterile now, because it's close to boiling temp, so any air that did manage to suck in, has nothing living in it. Eventually the lid sits on the jar, it sucks in, cools, so it sucks a little harder, and seals, then you tighten the screw cap and it's sealed for good now. You do NOT want to leave too big of an air gap on the top because too big of a gap, means when it cools back down to water, there was so much more to condense, so .. so much more room to fill with... something...so itsucks a lot harder. That 'seal' is only good for 5 or 6 inches of vaccuum. If you go pulling say 13 inches because of the excess gap, it WILL suck air in from outside. If this air was in a hot pot, no big deal, if this air was from your countertop area because the jar was taken out, and its cool air, it could be an issue.
Aaron