How do I remove a box that is being repeated on every sheet in my workbook

I was attempting to create a pivot table - and failed. In the process, a box appeared on the worksheet during a drag operation.
It cannot be removed by anything I have tried - and worse, it has repeated itself on EVERY sheet in the workbook, and is automatically added to any new sheet created in the workbook.

How do I remove it?

Click edit below your question and use the paper clip to upload a sample file (remove all sensible data before).

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