A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Hi JeremyHaywood,
It seems that the lag only happens in Excel but it does not affect any other application.
I suggest you temporary close all 3rd party applications/processes, and open Excel in safe mode to disabled add-ins on the Surface Book to ensure the issue is not caused by the compatibility problem with 3rd party apps.
Press Windows logo key + R >Type excel /safe to launch Excel Safe mode.
If the issue still exists, you can try to run Online Repair. Follow this article of Repair an Office application. Also to check if you have already installed the latest version of Office, check it in File > Accounts and share the version with us.
Regards,
Eli