When the document doesn't show in the upper window it means that something interfered with the commenting tool launching Excel to display the comments.  As a result the lower window cannot pin the comments, which is the cause of the red X's

Solutions:

If you are using MS Office 2013 or Office 2007, then it could be a file associations problem.  Please reference the following technote for checking and adjusting the file associations.

If you Client is 5.9 or earlier and you are using Office 2016, the problem could be a compatibility issue. The 5.9 client on your system was released before Office 2016 so there is a possibility that there is a problem with compatibility.  Check the version of MS Office and the file associations first.

Users with Windows 10 run into this blank commenting mode window if their display scaling is set above 100%. You can check this setting by clicking the windows icon in the bottom left of your screen and clicking on the gear icon (settings) and clicking "system" in the dialog that pops up afterward. On the left will be an option for display settings if it is not currently selected. In display settings, there is an option for the scale and layout which can be changed. Using the dropdown menu, we recommend changing it to 100%.