Okay...going out on a limb here. Are you vaping the same juice continually? I know I'm guilty of vaping too long on a particular juice and my taste buds end up getting bored with the flavor. And eventually, all I taste is cooked sweet juice...So I change flavors fairly often. Like I run 3-4 flavors in various mods all day long.
I've ruled that out.
I ran Hummingbird Nectar for a little, and it lost it's taste...returned every time I dripped, but not bottom-fed. I switched to some other KBV juice, dripped to sample and it tasted good, so I filled up a bottle and screwed it in. Flavor gone again if I bottom-fed it.