Sounds more like just a drain problem.

Make sure dust is not impeding the water flow at the drip tray.

Flush the tubing with a 10% bleach solution. Let it sit for 15 minutes and then do it again. With luck this will kill any algae in the tube and let you flush it out. Just be careful to not overflow the drip tray and wear old clothes.

A turkey baster comes in handy here.

When all cleaned check that the water flows quickly down the tube.

Clean the freezer floor to the drain to ensue that defrost water will flow quickly to the drain and not get a chance to freeze. Sometimes a coating og wax or just wax from a crayon then buffed up will help with draining.

Sometimes all the above do not solve the problem.

There is a jiggery pokery fix that works if you have a calrod (dark ceramic) heater. Take a length of bare 12 gauge copper wire, wrap it once or twice around the heater. Then the other end goes down the drain a couple inches.
Then when defrost comes on the wire gets warm and also defrosts the drain.
Not a bad idea to check that it just gets warm as you do not want to melt your drain.