Our Tech Support (Apophis) guru tested and replied as follows:
Regards,I'm not seeing an issue server-side. Everything is working properly and the uploads are getting processed without any issues. I would recommend that the user try different web browsers, Chrome, Edge, IE, Firefox, etc. If the issue persists across multiple browsers I would wager it might be a local antivirus/security issue that's preventing the file from being uploaded. I would also make sure any pop-up / ad blockers are temporarily disabled as well to make sure that's not contributing to the issue.
It's working fine for me on a Mac w/ Chrome though!
Doug