What tank are you using? Are you using drop in coils? Are you replacing with "new" coils? Is your PG/VG ratio the same with these new flavors?
I don't know much about the Dollar
juice club, generally. If they are inexpensive flavors, I guess I might consider it a possibility that some ingredient/flavor may be sup par in performance, but honestly, unless you've got a widely divergent PG/VG ratio, I'm having a hard time figuring out how a juice in particular could cause popping and spitback, that often tends to be a wicking issue or a wattage issue.
I'm not questioning you that this is in fact the case, but providing a few more specifics might be helpful in trying to identify the problem and etc. I haven't heard of a particular juice causing popping and spitback. If it's a thicker juice, though, than you are accustomed to (or even perhaps thinner), I might see it as a possibility that the mix in particular of PG/VG may be causing issues. If you haven't yet, I might play around with wattage and airflow some.
Is it also happening across tanks, if you have more than one? Hopefully with some more information, it could be possible to try and narrow things down into something more helpful and worst case scenario, if it's isolated to the juice, at least you got tester sizes, and will have found out, if nothing else, that the juice isn't for you.
Good luck I hope you can provide a bit more information and that you can get the juice working for you.
Anna