Problem with the Tanks is that they aren't very accessible to clean and the construction makes them difficult to dry after cleaning. Generally, the problem when they vape "skunky" is that the juice is gunked up on the coil and wicking material or the atty isn't wicking your liquid and Coffee liquids are probably the worst.
The darker the liquid, the more particulates that can gather up to goo inside the atomizer... yeah, I loved coffee liquids, hated what it did to my atomizers!. You might need to do a PGA rinse with a heavy coffee liquid every few days as maintenance. Some also do a dry burn to the coil to break away stuck burnt particles. I solved it by only using coffee in one atty (knowing it wasn't going to last long) and finding a new favorite liquid to vape all day in another atomizer.
The way the tank atty is constructed is with a wicking material that is just inside the spike. Its length continues to run below the spike to deliver liquid to the metal mesh which is above an atomizer coil that has more wicking material. That gets full of liquid quick, and like Terraphon said, acts like a cork.
The only quick semi-fix that might get a badly wicking atty working again is to GENTLY push into the center of the spike to move the wicking thread down a tiny bit so it has better contact with the internal bridge (a bent out paper clip works fine but take care to barely push on the wick so you don't push it all the way through).
Seems this atty is sensitive to cleaning and while some say they clean them and get them back to running fine, many report killing an atty that was working before the cleaning took place. Another issue seems to be blowing through the atty through the top (which seems to displace the wicking material in the center spike), so many say to only blow them out through the bottom battery connection end.
Some are having luck pulling the spike, cleaning and replacing the center wick in the spike (sometimes called a needle) and then cleaning the metal mesh by boiling or using PGA to soak and then letting the alcohol evaporate and then putting them back together. YMMV...
If it doesn't work, you can always leave the spike off and drip with it. At least you'd get some use out of it?
If you are like me, you don't want to fiddle with an atomizer that much

consider it toast and break out a new one.