In the German support forums a user reported, he wasn’t able to hide the sidebar, even if no widget is used.
I looked into your other theme Seos as it seems to be related and found a customizer menu Sidebar Options. I guess, it is a bug that this menu is missing in Seos Music?
]]>cannot modify header information error when adding or deleting plugins, editing menus, etc.
]]>When we click on the edit page the background is bleeding thru and
covering the words making editing impossible.