An inner cover below the Hive Top feeder can restrict bees going up to feed.
An Inner Cover above the Hive Top feeder can mold very quickly due to moisture.
Remove the Inner cover and place the Hive Top feeder in a shim you can make at home. drill a few holes in it and cover them with #8 Hardware cloth. This will let the moisture vent and keep mold from developing under the main cover.
Hers is mold forming on the main cover. You can wax it to seal it from moisture