Depending upon your particular
vaping technique, and other variables, it sounds like it could very well could just be condensation that runs down the air tube.
I noticed that happening on some of my early gear, some more than others, and started letting off of the button at least a second before I stopped drawing on the carto. I only get a slight residue of tiny droplets most of the time, now.
Also, since not all vendors seem to agree upon what a CE5 is

facepalm

, if it's the changeable head style, you could have a leak at the base of the head, if it's not secure, or the o-ring is damaged.