Mold on underside of attic flooring
How old is the house?  What you really need is the attic to be air sealed from the house.  paper backed vapor barrier on one side of the insulation as the only vapor barrier isn't going to be effective.
The typically standard is 6mil poly installed before the drywall.  Retrofit is going to be difficult - remove all the insulation and install continuous poly in all the joist bays.  Tape all seams.
Moisture coming out of the house will condense on the first cold surface so putting the plywood right after the insulation allows it to collect there.  Possibly removing the plywood would allow it to be vented out but moisture getting into the attic is still bad and ultimately the air bringing the moisture is costing you in your heating bill as well.