MS Word V16.47 automatically copy paste unwanted earlier text when I type fast

Hi, MS Word will randomly auto add text (from an earlier part of my doc) especially when I type fast (am using MacBook Pro Mac OS V 10.15.6). So I end up having to delete, or worse if I don't check my document carefully, there will be chunks of unwanted text in inappropriate places. Can someone help advise me how to fix this problem? Thank you. Jean