this is not my Technic,here is from a quick search look at the 6min mark.I notice that rda is designed for dual coils. Are you aligning the airflow holes properly with the coil?
Are there any hotspots in the coil? ie coil not firing evenly from the inside out.
I personally would yank out the build and try again. Wire is cheap compared to the misery of a build that is not working.