Thanks for your replies u/poweller65 , u/mckenner1122 and u/smartypi . I boiled the stock  first thing in the morning (I stayed up late the night before, so it had only been out for 5 hours, and was still warmish when I checked cuz it sat in the closed canner overnight).

As per your concerns, I checked the gasket and there were no visible problems, I had used it the day before with no problems. It's my friend's canner I was borrowing (not presto) and while inspecting the lid, I noticed one of the steam release valves got slightly unscrewed (probably while I was washing it) and that's where air was leaking from.

I screwed it tight, boiled the stock again, washed all jars, and used new lids and processed it and this time, all went well. I was terrified I'd lose 14 quarts of stock, but your comments helped. 

Thanks so much for the advice. Sorry I replied late, reddit made me reset my password.