A family of Microsoft word processing software products for creating web, email, and print documents.
Since this issue seems to be very unusual, it would be difficult to suggest a direct solution.
Does this happen only when you work on one particular Word document?
Check if the issue occurs when you work on other Word documents, and also check if it happens in a new Word document.
If it happens in all Word documents, open Word in safe mode and check if the issue reoccurs.
a. On the keyboard, press the Windows key + R.
b. Type winword /safe in the Open box, and then hit OK.
If it works fine in safe mode, then the issue may be caused due to a damaged add-in. You may disable the add-ins and check if it works fine in normal mode.
a. In Word, click on File, and then click on Options.
b. Click on Add-Ins, then select Manage - COM Add-ins at the bottom, and click on Go.
c. Uncheck all the listed add-ins and click on OK. Then close and restart Word normally.