Hey there,
if it was left being exposed to sunlight, taste will suffer.
if it got left opened, taste will suffer.
if the mixer made a mistake, taste will suffer.
if expiration date has passed, taste might suffer.
+ I also bought some 50/50 juices that tasted great, tasted the Max VG from the same company
and it lacked the flavor.. Maybe if it's a higher VG Mix, they forgot some flavor shots, it could happen.
You might be able to get a refund if you're really convincing.