I’ve seen quite a few users who ended up with just the top bar in edit mode after upgrading EPiServer lately. Most of them seems to have to do with the Visual Studio Web Accessibility Checker, or with Browser Link.

For me, however, none of them solved the issue, and it took me a while to figure out the reason. I had similar errors as the above, with the console full of dojo script errors so my first action was to enable client resource debug ny adding this to the episerver.framework section:

<clientResources debug="true" />

I ended up with a slightly more readable error cause:

Error: "scriptError"
makeErrorhttp://xxxxxxxxx/EPiServer/Shell/11.4.4/ClientResources/dojo/dojo.js:119:15errorDisconnectorhttp://xxxxxxxxx/EPiServer/Shell/11.4.4/ClientResources/dojo/dojo.js:1669:21 dojo.js:1834:4
src: dojoLoader dojo.js:1837:6
info: 
Array [ "/EPiServer/Shell/11.4.4/ClientResources/epi-cms.component.Media.js", error ]

The reference to epi-cms.component.Media.js got my attention. I know for sure i have i component on my site that make use of that component. A quick look later the component was found:

[Component]
public class CustomMediaMainNavigationComponent : ComponentDefinitionBase
{
    public CustomMediaMainNavigationComponent()
            : base("epi-cms.component.Media")
    ......
    ......
}

Once found, the solution was only 2 characters away. A while ago EPiServer changed the dot-notation to slash-notaion. So all i had to do was to change the code above to:

[Component] 
public class CustomMediaMainNavigationComponent : ComponentDefinitionBase 
{ 
    public CustomMediaMainNavigationComponent() 
            : base("epi-cms/component/Media") 
    ...... 
    ...... 
}

And the edit mode came back!