I'm experiencing a strange issue with Microsoft Excel (Office 365 MSO 16.0.11126.20234 32B) and Windows Defender running on Window 10 Pro (1809 Build 17763.253 64B) . When I save a macro-enabled Excel (.xlsm) workbook that has been open for a while it takes about 12 seconds to save the file (not acceptable). If I turn off real time protection in Windows Defender then turn it right back on the same file takes 4 seconds to save (acceptable). It will save quickly like that for a while then eventually take over 12 seconds until I flip the real time protection on and off again.
I have cloud-delivered protection and automatic sample submission off in Windows Defender thinking it would eliminate sending the file anywhere. Closing Excel and re-opening the file has no effect. It is not my VBA code as the same issue is seen when I comment out the code and just use the built-in save functionality. The only change I make to correct the issue is turn real time protection off and right back on.
Here is a 1 minute video (watch the immediate window to see the time it takes to save each time): https://www.screencast.com/t/gKOt7LNhsaxc
Also, at the end you can see I have both .xlsm and xlsm files in the Windows Defender exclusion list so I would expect Windows Defender to completely leave these files alone, but that obviously isn't the case. I'm not sure if the exclusion extension should have a period or not. Or if it should be *.xlsm (I can't find any documentation on it.)
I have a number of people using these files who are complaining of the long save time caused by this issue. Most don't have admin rights so can't flip the real time protection switch.