This is very confusing (would have guessed hardware but other juices seem OK?) Would have also guessed VG/PG ratio. You mentioned something that implied building your own (RTA, rda) It really does sound like you have good experience with this (including DIY juices) and you say this is happening with "drop-in" coils? As usual, more info (tell us everything... be specific) What tank, what mod, which coil (do you know what metal it is... Kanthal, Ni80, SS?) TC or regular power mode (watts) Do you get vapor even though the flavor is off? It's the old "20 questions" game... even small details might help us figure this out. Does the mod read correct resistance, do you keep checking that the wattage hasn't changed (are the mod settings locked)?