Try creating a fresh layout?
In the blank area of the problem layout, when you mouse over is there an indication it is clickable or hover text that shows?
There's no clickable or hover text that shows when I mouse over the problem area.
I think I tried to create a fresh layout last year <wink>, but I'll try it when my AM backup completes.
Update: I had tried creating a new Output (SSL), but not a new screen layout. I created a new SSL called "FreshNewDR", went to its properties, clicked Customize Selected Layout and selected Charcoal_Grey. I clicked Ok and got a message saying Charcoal_Grey already existed and to change the name so I named it "Charcoal_Grey2", clicked Ok, selected Charcoal_Grey in the drop-down in the "Manage Layout" section of the Responsive HTML5 Settings window, clicked Save and Generate, and I now have my icons showing!
Another Update: I compared the Charcoal_Grey folder to the (new) Charcoal_Grey2 folder and found out that all the files are duplicates except for "MasterThemeSchema.xml". I used the Diff Checker website to compare the two files.
Final update: I tried to upload a graphic of what Diff Checker found but the JPG was too big for the forum. I copied the "MasterThemeSchema.xml" file from the Charcoal_Grey2 folder to the Charcoal_Grey folder, thinking it would fix the Charcoal_Grey layout, but it didn't. I am just going to use the "Charcoal_Grey2" layout since I know it works!