Client Error - Arrow keys don't move between cells (Not Scroll Lock Issue)

Hello, 

Not sure if anyone else as encountered this issue. 

I have 2 client pc's running office 365 and randomly during extensive Excel usage their pages will almost freeze/lock up and their arrow keys no longer move between cells. Please note this is not he scroll lock issue where it changes the arrows from moving between cells to moving the whole page. 

Once the issue occurs the end user must change tabs or workbooks & return to the original workbook in order to continue working. 

Any thoughts? Solutions?

Thank You

~Crow