vinegar is a good tip!I wipe the rims of the jars with white vinegar - it is a tip from the Bell Book of canning. The vinegar will remove any oils on the rim. Probably a tip from the pressure canning meats section, but I do it for everything.
@ronott1 Glad you have had such success with canning.
As kids, We always hope that mom would have a non-sealed jar so we could eat it right away for snack or supper. All that hard work and we never got to eat any of it until winter.
I've had some weird stuff happen. All Operater error I'm sure. I had a friend help once and I ended up with a jar that didn't seal. We were disappointed until I took off the rings and found out she had put 2 Iids on it, lol. Another time I had a quart of soup siphon off almost 1/3 of the broth but it still sealed.
My worst issue has been not having the jelly not set hard enough. Jams nearly always work.
If the jelly goes too runny, I use it for syrup!