Co-Authoring breaks for Word Docs uploaded to SharePoint 2016, but works if created in site

[stephenakearns]

Summary: Word docs uploaded to our internally hosted SharePoint 2016 site can never be co-authored, but if I create/start the Word doc directly in SharePoint, then it can be co-authored. Why is that, and how do I fix it? 

Today if I create a Word doc on my Windows 10 desktop with Word (Office Desktop Professional Plus 2016) and then upload it to a SharePoint 2016 site, if I have the doc open, other users get an error message saying "UPLOAD FAILED This file is locked for editing by [NAME]." <SAVE BUTTON> (Side note: other person was using latest Mac version of Office)

If I got to the same library, and click "New >> Word Document" and copy the same content into the document, save it and share it, others can now begin co-authoring. 

I've reproduced the issue with multiple users, multiple SharePoint sites (all same SharePoint server). Why does the creation location of the document make a difference for co-authoring? Is there a fix for this? 

[#2]

@stephenakearnsMy guess is that it probably has to do with the version of Office that you are using on your desktop. A lot of our users are still on Win 7/Office 2013 and the only way they can co-author is to open the document in the browser. I believe Office 2016 allows co-authoring in the desktop app.

If that's the case, then just have users open the doc in the browser to allow co-authoring, open in the desktop app to prevent it.