So, 2 days ago I made 3 bottles of eliquid. 1 of which is strawberry, and is fine, 1 of which is TFA dragonfruit (10%) and TFA Menthol (somewhere around 3-4%), and another bottle of the around the same amount of dragonfruit/menthol. In one of the bottles some wierd goo stuff formed at the top of where the liquid was, stuck to the sides of the bottle (not "floating" on the liquid). Kind of worried to vape this, left some pictures below.
http://imgur.com/a/zCh03
The bottle with the cap on is the one that has the same mix, but looks fine.
EDIT: It's around 70-75% VG
That's the menthol crystals forming and separating from the juice. I used to be hardcore into The Vapor Chef's Zero Centigrade and if it got too cool the menthol would crystallize out of the mixture. A warm water bath and a good shake should fix it right up though.
Thanks. Kind of wierd how only one of the bottles got affected though, they're all stored in the same place.
From your post it feels like one bottle has more menthol than the other. Nothing sounded too exact in your post. The bottle with the higher concentration of menthol is the one that crystallized.