Yep, I've been there.
I've had acid reflux for years and years before vaping, I've previously been on OTC omeaprozole daily for a while. I'm a year off that regiment, give or take. Just some background for you, because I believe that the heartburn I was getting while vaping was different than my good ol' know-it-inside-and-out reflux that I've become accustomed to. Kind of. This is all anecdotal, take everything I'm saying here with a grain of salt, I'm the furthest thing from a doc.
Another note, something that may or may not play into it: I dipped for about 3 years when I was in the service. I also learned from the get-go to gut my juice. (yeah, I know, I know) After a few years, it probably lead to that acid reflux I was talking about, which didn't go away after I quit dipping. I maintained it while smoking with the meds, and made the switch a couple years later.
At first I figured it was because I was dual-using - both vaping and smoking. This was going through my daily med. So I cut the smokes totally, upped my nicotine level, and it went away.
When it came back after a few months, I lowered my nic level again, and it went away again.
Rinse and repeat until a few months ago, when I had to step back up to a reasonable nicotine level to steer clear of the stinkies. It's been about a month or so now back on much higher nic levels and I haven't gotten the "hot burps" yet, so... maybe the nic level has something to do with it, maybe it doesn't. Maybe in a month, or a week, or tomorrow it'll come back - I don't know. I know that I'm not taking my OTC for it, haven't in a long, long time, and I've stepped back up in nicotine without getting it again.
But in the past, whenever it would flair up, I would step down my nic level and it would go away. In my head, it was because I was getting nicotine into my stomach - vape clings to mouth, drink coffee, water, whatever - nic gets into stomach. From the years of gutting my dip spit, I think my once-iron-clad stomach is a little bit of a dainty snowflake when it comes to nicotine. Maybe I've moved beyond it, who knows.
Alls I know is what happened to me, how I took care of it, and what may have lead to it even being an issue in the first place.
Best of luck.
edit - clearing it up a smidge.