After 19 months in the freezer, I detect no change at all in any of my stored nic.
If the mason jars are like mine, with rubber gasket, the PG or VG might leach plasticizers. Might end up with rubber tasting juice. And if there is any PGA in it, that will happen even more. I think its best to use bottles designed for organic chemicals, such as the SpecialtyBottles amber or cobalt. The eurodropper insert acts as a nice gasket. Be sure to leave about 1 mL or a little more of head space. I had a bottle of 100 mg VG that was filled right to the rim. Didn't expand in the freezer, but it did expand a little when I brought it to the temp of a rather hot office and made a bit of a mess on itself when I opened it. That was a "now don't do anything stupid" moment. Gloves on, paper towels, made a couple juices, problem solved.