Old version of file opens after emailing a file

We have a fillable PDF Form to fill out for users, i filled out the first one with all pertaining info and did a save as and saved it to a specific file, then i grabbed the same file and changed the name in a fillable field, did a save as again to save the new files, i did it 3 more time all grabbing the original file as most of the fields didn't change. After this i sent out emails each file to the respective person, verifying that all PDFs were correct. However users reported that when opening the file, for some time it still showed the original name, then loaded with the correct name. I was able to replicate the issue by sending them again to a different email