YES YES YES!
I have NEVER had a problem with flies until I started vaping in my apartment 6 weeks ago.
I like dessert flavours so my liquids are always sweet and usually 70/30 VG/PG.
In the last month, I have noticed a sudden insurgence of small flies. At first, I thought that maybe I had a problem going on in my kitchen, so I have been keeping even cleaner than normal (to the point that if someone spilled a bit of sugary coffee on the counter, immediately wiping that up). But nothing is helping, and I notice they are hanging around the living room, where there is no food, ever, but I do vape there. And when I blow a cloud, they start dinging off of my face!
THEY ARE DEFINITELY ATTRACTED TO SWEET VAPOUR. It has nothing to do with keeping the caps on your bottles, THEY ARE ATTRACTED TO THE VAPOUR. And vape mist attaches itself to surfaces (look up vaping indoors), so you may have a sweet coating on your walls, furniture, etc. One time I didn't wash my hair for 10 days (I know I'm gross) and when I wet my hair and put shampoo in my hair, I could smell vape liquid IN MY HAIR!
These flies are the kind you would see around your overripe bananas, but they are not fruit flies. They are a tiny bit bigger and faster.
I am 100% convinced that vaping sweet e liquids indoors attract these little assholes.