I wanted to give this a bump - I just received samples from another excellent vendor, and all of the tart fruit flavors cause really bad burning, as if I had a really terrible acid reflux attack. All of the other flavors are fine - tobacco, dessert flavors are okay, just the tart apple and berry flavors do this to me...It's a bummer, as some of these juices would have been all-day vapes for me...
Although I don't have an answer for ya, I, too have had the acid reflux
occasionally with vaping. However, I haven't yet vaped any tart or berry flavors, but, that is not to say that any of the flavors that have caused my acid reflux didn't contain some type of citrus flavor. I usually just take an antacid when I'm experiencing it, and I can keep vaping away with the offending flavor

. The only conclusion that I can come up with is that there are certain flavors out there (whether it is by FlavourArt, P.A., etc.) that doesn't "agree" with some of us. Certain spicy foods mixed with certain beverages do it to me as well.
Just wanted to let you know that you aren't alone with the acid reflux. I guess it is part of the "trial and error" part of learning which flavors suit us best.
Good luck and Happy Vaping!