You need to follow the Bosch advice and give it a good long defrosting.....not just a couple of hours. It might be worth checking out the rear of the appliance. There will be a tube leading from the bottom of the rear wall to a container on top of the compressor ( motor ) Its worth taking this off and seing if its blocked with a jelly like substance. If it is , clean it out and refit it.
From your description , i suspect the freezer drain hole is blocked. Is the clear ice build up pooling in the base of the freezer compartment , under the bottom drawer because if it is , thats a classic sympton of a blocked drain hole.
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