I haven't read all the thread, but I did read a lot of it.  I have been making my own juices and using plastic bottles.  I'll get my juices flavored just as I like them and by the next morning, they taste nothing like I mixed them.  I know some people say to let them steep, but that is supposed to improve the flavor I thought.  I was thinking it was the sweetener I was using (100% pure sucralose diluted) that was changing the flavor.  So, I mixed some without sweetener and it tastes just like the one mixed with it, just not as sweet and they both taste bad after adding a lot of flavoring (white chocolate).  The flavor is basically gone.  I add more flavor and after a few hours, the flavor is gone again.  
I have 3 bottles sitting at home right now, one with sucralose, one with stevia and one without.  All in plastic bottles.  This is a sugar cookie flavoring.  I'll see when I get home if they all taste the same.  
What made me think it might be the sweetener was that I had the sugar cookie made just right and vaping on it all evening and when I woke up this morning, I started vaping it and I noticed I could hardly taste it at all.  Now, I did have it in a giantomizer, which I believe is an overgrown CE2 which is also plastic (I think they all are)  So, I'm confused really on what is causing my flavor loss.  I think I'll order some glass bottles and mix the same thing in all three and try the sweetener experiment again and see what happens.  
I'm glad I found this thread.