Unable to extend offer letter on uploaded/edited offer letters

Summary: Mac user on Big Sur version 11.6.5 is having issues with editing and uploading offer letters. They get error message " Job Offer can't be extended because of the job offer letter wasn't created by the BI Publisher server."

However if another user redrafts the offer, removing the letter attached and reattaching the same letter (the letter was downloaded and resaved to their machine (PC), modifying the name of the rtf), submitted, previewed and extended without issue.