I can confirm this as well actually. Also its a coincidence that I started growing a beard rather than shaving religiously, less acne and bacteria goes elsewhere. I have been vaping 2 years however and about the same time as beard came in, 6 months ago I started getting ulcers too. But lately its been making my top of my mouth sore, so I can relate to the reason why.
Lately I've been going up in power and doing rebuildables more, so that excess juice spits out all in your mouth, burns as well, and causes openings for sores to form.
Advice to you is to watch the spit back as best as possible. Also watch the tip of your tongue. I did it without even realizing it, so hope it helps someone.