I just went though a similar taste problem. I have had so few colds and sinus problems since I started vaping in June that I forgot what it was like. Two weeks ago my favor flavors started tasting like nothing. This was bad because I had just got my first mod - The Copper. My Ms. T's, Eggnog, my first My Freedom Smokes order of Eggnog and several other favorites all of a sudden tasted horrible. On a 510, 901, 801 and tThe Copper. MFS told me about shaking the bottle and even though I told them I was starting to suspect a cold they sent me a new bottle (great customer service.)
Anyway, I tried burns, replacing atties and fully charging batteries and nothing helped. Either no taste or a bland taste. But, everyone I was around commented on smelling butterscotch, chocolate, coconut, etc. Which is neat by the way after spending years being told how much I stank like cigarettes.
So, this morning all the flavor is back, I am vaping some apple pie and ice cream from Ms. T's right now. (I never thought I would like any of the flavors...) Must have been a cold because I have been coughing and sneezing and the like of and on for the last two weeks. You may be coming down with something or your system may be in the process of adjusting. I know my lungs just did a bout of cleaning out during the last couple of weeks. And this is over five months after I started. Hang in there, shake your bottles pick a method to keep your atties cleannand don't stress. The flavor will probably come back.