I’ve noticed that in Safari, the form gives an error when submitting if the user does not attach a file.
The user is not able to send the form if he/she is not attaching a file to it. All works if user selects a file to upload. If user doesn't not select a file it gives error "An error occurred processing the form. Please try again". File upload is configured to be optional.
Works in Firefox and Chrome, but not in Safari.