Self-defrosting??? Did that expert repairman turn OFF the freezer??
My residential fridge/freezer in the B&M was leaking on the floor. Ice maker was clogging as well. Turned out to be a clogged drain for the self-defrost. It was frozen solid...that de-frosted water had to go somewhere.
If you can access behind the fridge, look underneath. There is a pan that captures the water that should be damp or wet. Check to see if it looks like it has had water in it recently. While you're at it. Run a vacuum under there...those dusted parts need air to breath.
You can also check for the drain hole in the back of the freezer, as well as the drain hose. Is either frozen solid?
I have another freezer, so I shut mine down for a manual defrost. Has worked fine since then.
Before going to such extremes, you may want to try a bit of hot water into the drain hole. Be very careful if you attempt to clear it with something like a cloths hanger (not recommended) poking a hole could cause a permanent leak.
Hope this is a simple solution that works for you.