I just had this happen today with some DK RY4 but I think I have a fluke of understanding. I had just put a new head on a clean Kanger T2 and filled from my known 50ml stash of RY4 and let the wicks soak for a few minutes but probably not long enough, and my eGo was cranked up to 4.2v, and I got nasty burnt nasty over and over and then still nasty after going to lower voltage until I hit 3.2v and not nasty but no vapor and no taste.
So I put another new head on and let it wick a bit longer and started light at 3.2v and then cranked it back up to my normal 3.8 and all is well again.
I might have had a bad head, or chared it up on those first dryish drags. But it got me thinking that the RY4 is the only thing I currently vape at that low a voltage. Most stuff has a sweet spot around the 4.0-4.2 range on my T2s, but I've always prefered RY4 around 3.8 and find it burny at 4.0 or above. So I'm thinking there might be something in the DK version that is crap when it's too hot and spoiled that first head.
So, either it was a bad head, or that high v gunked the wick up with nasty burnt stuff. I won't know until I try cleaning the suspect head which.
Did you by chance start off at a high voltage first? I think I'm now going to start new heads/juices at low voltage and move up just to be on the safe side.