"Upload Failed" after inactivity from Excel 2016 (MacOS).

[Martial Millioud]

I am pretty new to Confluence. We are very small company running Confluence 6.10.1.
I'm using Excel 2016 (MacOS). I have some page where we use Excel as template. If I click the "Edit Document" from Confluence page, everything is open properly in Excel, I can edit and save the document succesfully.
Problem start after a few minutes of inactivity in the Excel spreadsheet, if I resume my work and want to save, I get the "Upload Failed, We're sorry this didn't work, Try saving again later...". Only option is to discard all changes and reopen the document from Confluence. As the problem seems to start after a few minutes of inactivity, there is probably a session timeout parameter somewhere in Confluence side. As I am pretty new to Confluence, could anyone maybe direct me where to look at ?

Thank you !