Upright freezer door not sealing / staying closed tight

My upright freezer door won’t seal or stay closed. It used to “suck closed” after I opened and closed the door, making reopening difficult. Then the drain froze up. I melted the ice from the drain with a hair dryer and some warm water. Ever since I thawed the drain the door will not stay fully closed. When the compressor and inside fan turn on, the door freely swings open about the thickness of a sheet of paper. The door seal lines up perfectly with the freezer doorway. If I don’t lean something against the door all the time, my freezer will fill up with snow.

The same thing has been going on with mine. Have you come up with a solution? Is it as simple as replaceing the door gasket?

Also, My defrost tray is completely dry and my heating coil is extremely hot. Any assistance would be greatly appreciated.