What this will be done to is a blocked drain gutter inside the freezer.
What you need to do is either remove the freezer door and remove the baskets in there.
Then remove the ice maker
unit from the top in the freezer and then from there remove the back panel in side the freezer.
There you will see the evaporator, Under this is the drain gutter. This will be covered in ice. You need to pore boiling water in there and melt all the ice in there.
Then in the gutter you will see the drain hole. Again pore boiling water in there and poke something in there to fully clear it. Then test it by poreing water in there and make sure it drains away ok.
Once clear refit the panels and then you can close the door as normal and this will be fine from there.
But if you dont want to go removing panels then what you need to do is empty the freezer and turn the appliance off and leave the freezer door open for 24 hours. Place towels in there and the ice in there will melt itself and clear the drain hole.
Then afte the defrost this will be back to normal from there.
Try the above and see how it goes. But from what you say this is a blocked drain hole in the gutter thats the issue here.