It could be a touch of chalkbrood. Chalk is weather and genetic related, but also is considered a "stress" disease, which oftentimes means you see it in periods of damp cooler weather, or when the hive is thrown into turmoil (Divides, nuc building, etc.). Certainly housecleaning and the normal flow (duties) of this hive were effected by the die-off of the chemicals. Once chalk starts, the effects sometimes lingers for weeks as it takes this long for symptoms to be seen.
As the numbers rebound, they will slowly correct things like chalk, clean out tainted pollen, etc.
Give it some more time.
As the numbers rebound, they will slowly correct things like chalk, clean out tainted pollen, etc.
Give it some more time.