It sounds like something in your juice, since its intermittent. If you stop using that particular flavor, and the symptoms go away, well, I'd say you may have your answer.
I also view the juul with a hint of suspicion anyway. It seems some folks just LOVE the juul formulated juice far more than any other juice (including nic salt juices). To me, anything that INTENSE leads me to wonder what they used to convert their juice to nic salts, and what other possible additives may be in there.
If you find your uvula swelling after that, I'd consult a doctor. Could be an allergy reaction to something (vaping or otherwise, I will say, this year my allergies in general are slightly worse, and I do wonder if tobacco "'blocks" some of those symptoms, much as it can do with asthma symptoms. So, if it doesn't clear up, then see a doctor and go from there.
This may also be a nice opportunity for other vapes besides the juul. You may find something that just works better for you, and with less expense.
Best of luck,
Anna