The image suggests that the page loads some additional javascript widgets such as the 'Back to top' button. If one of these javascript widgets is broken it will prevent any subsequent widgets from loading and that may be the reason why the file manager isn't loading.
The additional javascript may be part of the Database preset in which case it will be in the Javascript tab of the activity and you can try removing it to see if the problem disappears.
Or, it may come with the theme you are using and you can try changing to a standard theme to see if the problem disappears.
Or, it may come from somewhere else and you can have someone use the browser developer tools to debug.
Or, the file manager problem is caused by something else. Hard to tell without inspecting the environment so try first the above.
hth