Error: Default Layout file is not exists with Helix Ultimate.
Learn how to handle template issues while rendering layout.
The issue related to special menu items that not assigned correctly with the template style id and it's caused the Helix Ultimate rendering the template layout for these menu items.
Example: You have installed a special template before and assign the special menu items for this template style (via Menu Item -> Details -> Template Style). When the template is uninstalled, these menu items no longer assigned to the correct template style id and it caused the issue with Helix Ultimate.
Just open the menu items that caused the issue with Layout Rendering and hit the Save button to update the Template Style ID.