I used to get "dud buds" often, especially after the first two weeks of switching over exclusively. After that, seems like I'd get it anywhere from after a few days to a week of vaping the same flavor over and over. Would happen with "new flavors" and flavors I'd enjoyed for awhile. I tried switching flavors often and sticking with one that "worked", I tried regularly brushing and using Listerine, scraping my tongue, lemon juice, vinegar, all which worked decently but only temporarily. I ended up changing two things and haven't had it since, except briefly after trying out a new flavor. I switched juice brands, and I started dripping exclusively. I too chain vape, and I've even been able to vape the same flavor for MONTHS witout "vaper's tongue" although I did get "burnt out" on the flavor and just don't care for it as much, but I can still taste it just the same. The other thing I noticed about switching brands, I can vape for days around the clock and my coils don't get "gunked" up like they were with the other brands I was using and yet I'm still using flavors that are typically known as "coil gunkers", custards and sweet bakery flavors.
My conclusions.....quality! The guy I mainly get my juice from now, uses 100% quality ingredients and the same stuff every time. I've found a few other brands that also are high quality and I now get the same experience.