Because you said strong vapors I am assuming you used more away or Formica pro?  What was your fall mite treatment?  And when was it?  And did you do a mite count afterwards to know it was effective.
fall is a big window.   You really need to start mite treatments in mid August, and then the bigger challenge is to keep more levels low until October.  
My experience is that a really strong hive in the fall can often crash overwinter.  Often the best looking bees in the spring looked somewhat mediocre in the fall.