Translator Role is required to view custom doctype form?

I have created a system user with no role except System Manager.
After log in, this user can’t open the form from custom app. Also can’t save a new doc (blank form is still displayed).
But when click on a doc, the form is a page with blank cards.

The doc list also not displayed correctly - no side bar and no search box etc.

In the browser console there is error msg:

Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'this.sidebar.add_user_action')

But when I assign the Translator role, it can open the doc form normally.

So I think this is a bug. Can anyone confirm this?