Is there a burning or burny flavor? Definitely that's a special, important and common category of flavor problems.
P.S. Do not use the Subvod tank on any battery other than the one it came with. Likewise only use the T3's on the small "stick" batteries.
Generally most tanks can be swapped between batteries with correct settings. However, you're right that the Subvod battery probably shouldn't be used for anything else, as it expects to connect to one of 2 specific coils only. Probably should have warnings all over it (although I doubt it will misbehave
that bad) ...
Actually, I don't like the preset small stick batteries very much because they tend to put out too much voltage for an EVOD, even with the 2.2 or 2.5 ohm coils. Yeah, I know they're made to work perfect, but they don't. Good for very short drags only. I don't like the 1.8 ohm coils and have no idea what they had in mind for the 1.5's (these are all Kanger single coil types).
Check for the SOCC coils (red writing on them), while cotton's improvement the box I got was very poorly made and they were good at first but didn't hold up. An internal shot of some others don't look as messed up as mine were though.
The plastic tanks can crack, but I've never seen that they negatively affect flavor before then. They can get a nasty flavor after a while (months) which a cleaning helps (airing out is also good). Water left behind can really mess up the flavor though, and doesn't seem to go away either (even though a tiny amount of distilled water well mixed into the juice doesn't seem to have the same effect). I need a new batch of EVODs myself, I have 2 mini Protanks which are glass but I don't like them as much, flavor wise they lack a LOT for some reason and they even get an off flavor to them faster than the plastic tanks. And as for the dual coil series, thoroughly unimpressed, I'm thinking of adapting my way-overpriced Aerotank to single coils as I hate it now... the duals do have less off-flavors, but at the cost of less flavor total even while consuming more power and juice.
Your ejuice could have switched to higher VG, which is thick and doesn't wick that great. I used to like 50/50 juices in my EVODs but but after using them less I find myself less willing to baby them, and need just a little more PG even if it means diluting an expensive juice... Or your vendor may be trying to make the exact same, but it is very easy to mess up.