If your microwave came with a defrost net, was it used?
Refer to the Owners Manual to see if your microwave comes with a defrost net. If it does, it should be used.
This will allow the item that is being defrosted to be raised up enough that the microwaves
can penetrate from the underside of the dish, for more even defrosting.
If your microwave did not come with a defrost net, it will be necessary to turn your food over during defrosting.