Have you gone through each activity, or module being used on your front-page? It seems to me that the block is "attached" to one of the sub-pages of one of the activities on the front-page course. It seemed like you may have already done this while looking for the block, but just in case I wanted to mention it. I am suggesting to navigate to each course activity and each sub-page of those activities, to see if the block appears within any of those contexts.
Jamie