Acetoin and Acetyl Propionyl (A/P). They are under pressure to get rid of it entirely so Cap have a policy of no DAAP in flavours anymore. The flavours that have been reformulated and are pending approval (independent testing to verify no A/P) include:
Coconut
Marshmallow
NY Cheesecake
Orange Creamsicle
Popcorn
Simply Vanilla
Flavours where reformulation is in progress:
Cake Batter
Horchata
Strawberries and Cream
Flavours still to be reformulated:
Blueberry Cinnamon Crumble
Blueberry Pomegranate with Stevia
Chai Tea
Chocolate Caramel Nut
Chocolate Coconut Almond
Choc Glazed Doughnut
Choc Raspberry
Cinnamon Coffee Cake
Dragonfruit
Dutch Chocolate Mint
Egg Nog
French Toast
Gingerbread
Hot Cocoa
Irish Cream
Milk Choc Toffee
Orange Mango with Stevia
Pralines and Cream
Waffle
There are a couple others, like Bacon, Crispy Bacon and Butter (not Golden Butter, just plain Butter) which are also being reformulated but have little application in vaping. Another exacerbating factor is that some flavours contain A/P even when they don't add it, probably as a result of natural occurrence and the extraction process.
They have most of their V2 flavours listed under the "Tested and certified with no A/P" category. So VCv2 is fine and won't be changed further. I have no idea about v1. It does contain A/P but they haven't listed it. I imagine they will just drop it eventually.
It's probably the way that all flavour lines will go. FA should be largely unchanged, Cap too after this reformulation round. Inw has problems with disclosure and are reformulating some flavours again. TFA will probably be OK with their DX even if they drop a lot of OG flavours, Flv have a few with high A/P. FW... let's not even go there.
A decent supply of VG, PG, Nicotine, some menthol and mint. I make bottles of plain VG/PG 80/20 with 3mg Nicotine to dilute my e-liquid when it becomes overbearing.
ITO commercial juices, I always keep a bottle of XXX by VM on hand. Lately I am also loving Panama by Wiener.