Hi @David P
Are you using OneNote for Windows 10?
Please note Q&A forum supports OneNote Desktop App, OneNote for Windows 10 is not supported currently, I suggest you post a new thread in Microsoft Answers Community --- OneNote.
If you are using OneNote Desktop App, please check whether this issue occur when you use pen on other programs.
Besides, please make sure your notes are stored online or backed up, then try to reinstall OneNote desktop app: https://www.onenote.com/download
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