This article describes the following warning that you might get if you try to open a page or post for editing in Beaver Builder when you already have a Themer Singular layout that applies to that post or page.
This post has a Themer layout assigned to it. Using Beaver Builder here will override that layout. Do you want to continue?
In most cases, this warning arises when there is already a Singular-type Themer layouts that applies to the post or page you're trying to open for editing in Beaver Builder.
In a Singular Themer layout, the Post Content module gets its content from the native WordPress editor. This means that you cannot use Beaver Builder for standard layouts on posts to which you want the Singular Themer layout to apply.
If you choose to ignore the warning and open Beaver Builder to lay out the content area of a single post or page that has a Singular Themer layout applied to it, the Themer layout will be overridden and won't display on that post. Your active theme will take control of all the areas of the page except the content area, which will contain the content you created in Beaver Builder.