Megan, the PG / VG ratios of the liquid you are using will be deterministic on how well your wicks will perform.
If you have too much cotton in the liquid channels and your juice is too thick, then you will encounter dry hits. This sounds like the problem you were encountering. Is the new juice higher in concentration of PG? This will cause it to have a lower viscosity and therefore wick better in denser cotton.
Just realized this (I'm vaping off of my ZampleBox from this month). The first juice I used is called "VG Heavy" (Liquid Sin - VG Heavy). The newer juice I'm vaping on ... well, I can't find the info for PG/VG ratio, so I can only assume it's higher PG than the first juice. (It's Fairy Blood - Good Life Vapor)