Long story/short- The screen is not dried properly.
Long story - As we know humidity plays a big role in screen exposure. If the humidity is too high in your area you need to invest in a dehumidifier. Even if you use fans to dry they are only drying the room to the level of humidity it already is. They are in essence pushing around wet air. When this happens the emulsion will skin over and dry to a degree but not be fully dry.
Emulsions are +-70% water. The goal is to evaporate all the water so the solids can link with the mesh. When water is trapped in the emulsion it can have a slight rubbery yet dry feel. This moisture will bond to the coating on film positives. Hence they stick, and the ink on them can even come off onto the emulsion.
Get a dehumidifier for where you coat and store your screens. Make sure the humidity level in this area is at or below 30% for optimum drying. Be sure to empty it on a regular basis or it will be putting wetness back into the air.
If you cannot do this try reversing the image when you print it and putting the non-coated side against the screen. Caution- this will put a film layer between your art and the screen. Fine for spot color printing but not recommended for high detail images.