If you haven't done so, consider seeing a gastroenterologist. GI tract issues, including GERD, can trigger bad or sour tastes (related to acid reflex) and weird changes in salivation. Just a thought if ENT and oral care practitioners get nowhere. I had something different, but also unusual, and saw a bunch of specialists to no avail. I later mentioned it in passing to a gastroenterologist and he immediately named it and we fixed it within a few weeks. It never occurred to me that this could have been related to stomach stuff.