animated circle (hourglass) does not stop

Generally this indicates that the process is getting stuck on the email notification, meaning wp_mail() is not completing.

Any tips on how to fix this?

BTW the file does upload — I found it in wp-content/uploads/simple-file-list/

Can you confirm that the upload process hangs when uploading from the Admin dashboard side? No notification is sent from the back-side, so if it still hangs that is not the problem.

Yes it also hangs up when uploading from the admin

Try it at:
https://midwestawma.org

The “File Transfer” link is near the bottom.

or go directly to
https://midwestawma.org/file-transfer/