One other possibility to consider - Aren't a good part of vape juices made from organic substances ? - And don't all organic substance go bad after awhile ???
{even canned food kept in a vacuum has a limited shelf life}. So is it possible that is why it went bad ?
Also, you had mentioned freezing - doesn't the freezing do something to the flavor after you thaw it out ? And, if you freeze in a glass bottle aren't the glass bottles prone to crack sometimes do to expansion of liquids when frozen ?
Yes, anything is possible. But that taste of the juice and the fact that it made me sick made me think it was chemicals from the plastic bottle. Even if LDPE is technically "food safe", I doubt any of those studies tested it with nic. Besides, these cheap eliquid bottles, who knows what they are really made from. Regardless, I'll err on the side of caution and I don't trust plastic for long term storage of anything, really.
PG & VG don't freeze at the temps our home freezers reach. Here's a page I found on a UK retailer's site about freezing eliquid.
Does E Juice Freeze | AquaVape UK
For the most part, glass jars and bottles break in the freezer because what's in them freezes solid and expands, causing the glass to crack (this can happen even if you leave plenty of head space, I found that out the hard way). However, it is possible for glass to break just by freezing it, but it's not very likely assuming the glass is not put in the freezer when it's warm/hot or thawed quickly.