That's new to me. I'd say perhaps you're having an allergic reaction. If that's not the case, then the vendor is doing something fishy or dangerous. Either way, just stop vaping the juice in question. Also, are you positive its from ejuice in general? Are you eating/drinking anything during the vapes? Has this happened to you before? How long have you been off cigs? Many people have unique symptoms of switching over to vaping for good, although I've never heard of the mucous buildup tbh.