Well, here's the deal ... there are just a few variables that it can be. I am thinking that the coils may be slightly shorting.... I had a problem similar to that with my Kennedy RDA....... Or, they could have wound your coils totally wrong, in which case you need to return to the vape shop and shove the RDA up their ho ho's .......... I seriously doubt it is the cotton because I imagine that your are using organic cotton. So, when you think about it, the only two possible things it can be are the coils or the juice. You can pretty well eliminate the juice since you have used it prior to that. I am thinking that it is either wound improperly or it is shorting against the top cap of the RDA.
Pretty good sum up,
@lanye take your wicks out of the atty and put the chimney on the build deck and press the fire button. See if any certain spot of the coil is glowing too quickly or too bright. Coils should heat from the middle <-> outwards. If it's touching the side of the chimney, you can move it inwards a couple mm with tweezers (don't use metal tweezers while firing the coil) if it's touching the inner sidewall. If it's getting hotspots, pulse fire, pinch, repeat until said hotspots go away.
Edit: If no hotspots, get some new organic, unbleached cotton in there and wick it up the right way! And possibly clean out your atty before doing. Heat your coils up and use a wet (you're going to want a small cup of water to do this cause Q-tips dry up quick) q-tip and brush the coils with the wet side and then heat again, the water should sizzle off of them, clean out the deck underneath and definitely clean out the chimney/top cap under the sink.
Wait. Did you rinse out the machine oil before building and wicking it?!