This is caused by the humidity in the air (an issue for us in the tropics) which causes the paper to become damp and retain moisture. When the paper goes through the hot part of your MFD, the moisture is very quickly removed from the paper, as such will cause your paper to curl. Jamming is commonly caused by the curled piece of paper, trying to go through parts of the machine designed for flat paper.
Ways to fix this are not buying paper in bulk and letting it sit for a long time, or buying a paper warming cabinet to store your paper. It is also a good idea to only open a ream of paper if you are going to use it all to fill the paper tray. Try not to leave open packets of paper out for any period of time.
By following these tips you can also save your business valuable time and money.