Consider the following scenario:
You're using the classic view for a Microsoft SharePoint Online list.
You edit a list item that has an attachment, and you select the option to Delete the attachment.
You reattach the same file or a file that has the same file name.
When you click Save in this scenario, you receive the following error message:
Sorry, something went wrong.
A file with the name already exists.
To work around this issue, use one of the following methods:
After you delete the attachment for the list item, click Save. Edit the list item again, reattach the file, and then click Save.
Upload the attachment with a different file name before you click Save.
This is a known issue in SharePoint Online.
Still need help? Go to Microsoft Community.