I guess I was lucky, I didn't have any issues with the vapor changes. I started out with 24mg's of nicotine since I was a PAD or more smoker for over 40 years. Then, after about 6-8 weeks, just can't recall the time period, I cut it down to 18mg's. Now, I'm doing 12mg's and am very comfortable with the nic changes and am about to cut to 6mg's.
If you smoked menthols, I would suggest you try to remain on the menthol vape by itself for a while. I could be that your vanilla is causing what you are experiencing. Unless you smoked vanilla cigarettes, that is more than likely the change your lungs are experiencing in your issues. You have gotten rid of a ton of toxins and heavy metals by getting rid of the cigarettes, but you have added something new with the vanilla. It seems to me all this is a step at a time, or at least that's how I approached it. I was a menthol smoker, stayed with it for the first few months by itself. Now, I have added a few flavors, but I limit the amount I use of them, pretty much stay with what I had been doing all those years, menthol. For a bit of variety, you can use different types of menthols - spearmint, wintergreen, etc.
CD