I think tomatoes only need to go 25-30 minutes at 240°(10lbs pressure). so, cooking them a lot longer could cause that, I guess. make sure you are getting any air pockets out of the jars with a small spatula or something, and putting the lids on really tight by hand. I always clean the rim of the jar immediately prior to putting the seals on them, too. likely the ones that aren't sealing have stuff from inside the jar interfering with the seal. I never lose any liquid like that when I do tomatoes, and I do pressure can all of my tomatoes.