It could be that the filament is absorbing moisture from the atmosphere. You should always try to keep it dry by storing it in an airtight container with a drying agent with it.

To cure your current problem, put it in an oven at 40-50C (100-120F) for about an hour then store it properly.

You must also understand that the stepper operating the filament feed into your extruder is not very strong, so it cannot pull the filament off the reel easily.

Old Man Emu