Hello,
I am having issues with detailed excel spreadsheets after updating to Office for Mac 16.15 in July 2018.
OS X El Capitan Version 10.11.16
Excel for Mac 16.15
When I open the file, I receive the message below.

If I hit 'Yes', the next message is:

If I hit 'View', the message is:

The spreadsheet is now corrupted for other people to read (shared via dropbox).
Alternatively, if I open an old version (saved prior to the Excel for Mac upgrade), I get a security warning:

If I 'Enable Content', the file becomes corrupt.
This is only happening to a handful of spreadsheets and began when I updated to Office 2016 for Mac Standard via the Microsoft volume licencing centre.
Can you please provide advice?
Thanks