sounds like you need a new freezer seal gasket. not a hard project to replace it.
You have this problem because your doors seal is not working properly ! Make sure you don't have anything in the way of it closing well , if that isn't an issue , you will need to replace the seal .
I agree, it sounds like a seal issue. A retailer like Appliance Parts Pros will have the seal for the refrigerator and will most likely have a video demonstrating the installation of the new seal. I hope this helps!
You need to defrost it and then restart it. If it is beginning to do it again, you probably have a gasket sealer not working properly. It is not expensive and not too difficult to replace those gaskets when the seal breaks or they get old.