Help Nutrition GPA App can't export

[NewArtDroid]

This app is not allowing me to export my history, even though i have other apps that allow me to export comma-delimited files. I've been in touch the developer and they think it is a problem either specific to my phone (Droid Turbo 2) or Android version (6 v 5.1). The problem is that when I choose Export, it goes to the standard share places, Gmail, Dropbox, Evernote, create PDF, etc, but none of them work, mostly because it can't find the file, creates a zero byte file. It may be something with permissions. The developer has suggested various fixes around permissions, but nothing is working. Is anyone more familiar with app development able to help guide me or know what to tell the developer to address this? I can post screenshots if that would help. Please let me know if I should have posted this in the Droid Turbo 2 forum or the App Development forum.