I've ordered several bottles of Boba's at different times, and it was always the same to me. I have heard of consistency problems with it, but I never experienced it and it's been a while since I've ordered Boba's.
Having a bunch of different descriptions for the same juice is fairly common with "mystery" flavors like Boba's. Without having an obvious flavor, the mind kind of relates it to what it knows when trying to make sense of the flavor. My brain went right to graham cracker and got stuck on that.
Well, Wlad says it's graham flavor too, so you're probably right. However, it tastes clearly like oatmeal with raisins to me.
I think anyone getting ashtray flavor from Boba's, though, is tasting a burned wick or nasty coil.