Hi,
the result mail setting are stored in the #__visforms table in the field "emailresultsetting" in JSON format. It should look something like that, if the data are included in the mail and uploaded files are to be attached to the mail.
Code:
{"emailresultincfield":"1","emailresulthideemptyfields":"0","emailresultincdatarecordid":"0","emailresultinccreated":"1","emailresultincformtitle":"1","emailresultincip":"1","receiptmailaslink":"0","emailresultincfile":"1"}
Actually the behavior you describe could be explained, if this field (emailresultsettings) were missing in the database table #__visforms. This would explain both, that you cannot save the changes to the "include file" option and that the data are missing in the result mail.
Did you install Visforms for the first time (using the current stable version 3.7.6) or is this an update from an older Visforms version?
There is an install.utf8.sql file in the administrator/components/com_visforms/sql folder. In this file you can see the table and field definitions for Visforms.
Regards,
Aicha