A family of Microsoft word processing software products for creating web, email, and print documents.
I suggest running the Word app through Safe mode and check if an add-in or extension might be causing the issue. If it's a no go, you can repair the Office suite and check if it helps solve the concern. If the issue persist, try uninstalling and reinstalling Office 365. You can click on this link.
Update us with the outcome so we can assist you further.
Bob