Sounds like the 30ml bottles sit around far too long! They should be aware of the stock in/out dates, and they (all vendors) know that flavoring eventually goes bad by sitting around. Normally that takes a long time, like a year or so, but I'm sure some flavors spoil quicker than others.
From what I've read, maybe even at the TFA site too, is that when a flavor is bad is smells like a lot of alc and not much of the flavoring aroma is left anymore. They can also smell badly too, or no smell, but I think a majority will smell more and more like alc as they loose their potency, and then of course flavor levels drop off as that happens too.
I had a similar experience with GoodProphets and a 30ml of TFA during one of their sales, but I didn't realize that was the issue until a month or more later, so I didn't even try to contact them. It was either that, bad flavoring due to age, or they cut it with alc, not sure, but it was too late to even try to ask for a replacement by the time I realized the issue.