After you remove the loose insulation to other areas in the attic, remove the ceiling and install some faced fiberglass batt, stapling the flanges to the edge of the ceiling joists. Then you will have a new vapor retarder and insulation. Use the first layer as high as the joists, second perpendicular layer as per R-value for your locale.
That is only if you have to remove the ceiling. Only in very cold climates, do you need a vapor barrier in the attic. A special vapor retarder paint primer will also meet the requirements (0.5 perms) to keep the moisture from going to your insulation over the bathroom.
The solution to your problem is an exhaust fan, rated for your bathroom square footage. Bathroom Fan Sizing
Be safe, Gary