Fix here .  .. 

install of DNN 9.9.1 on an Azure app service. The wizard completed successfully and then the site showed a 503 service unavailable error. Checking the logs gave me the message that "The file '/Admin/ControlPanel/ControlBar.ascx' does not exist."

After a little while of frustrated searching, I discovered that the problem is that in the HostSettings table, the value for ControlPanel was set to '/Admin/ControlPanel/ControlBar.ascx' and needs to be set to 'DesktopModules/admin/Dnn.PersonaBar/UserControls/PersonaBarContainer.ascx'

Making that change and then restarting the site fixed the problem for me.