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.