Thanks. I figured I was overthinking it. My mom used to make candles in jars back in the day and I remember them popping down after a few days of jarring them. Was expecting the same to happen with the tobacco but didn’t think about the fact I wont get the temp fluctuation like hot candles or jam. Cheers
If the lid was put on while the wax was still hot, that would do it. As it cools down, the air that's trapped inside contracts, which creates the lower pressure than the air outside and pulls down on the lid (well technically, the higher pressure air outside presses down on the lid).
Boiling water is one way to seal them (heat the jar and lid, stick whatever in, close lid just finger tight so air can escape as it heats and expands, boil in water, remove and cool slowly). An alternative would be using a foodsaver type vacuum sealer, some come with a canning attachment.
Anyway, less atmospheric pressure inside than outside is what causes the seal and the pop-down. That's the only way to achieve that (trapping hot air and waiting for it to cool and contract, or using a vacuum sealer to remove air at room temperature). Simply screwing down the lid won't cause it to vacuum seal. The popping is because of the vacuum. Of course the sealing stuff on the rim needs to be in good shape too.
If the lid ring is on tight enough to prevent air from moving into/out of the jar, the lids can pop up or down depending on changes in atmospheric pressure and temperature, but that won't be a very strong seal the way it would if vacuum or heat sealed.