Copying multiple cells in Excel causes workbook to freeze

Hi,

I have a user running Excel 2016. They have two workbooks open on two different monitors. The user attempts to copy data from one cell to another within workbook one. The workbook freezes. Excel does not display a "Not Responding" error message. To unfreeze the workbook, the user has to click within a cell in workbook two on the other screen.

They are allowed to input data into each cell one at a time in workbook one. But when they attempt to copy data to additional cells, Excel freezes.

Anyone ever witness this type of behavior?