Can't save changes to search results layout in View Designer

On a new Studio project:

• Create a page provider in Modeler
• Edit search form layout in Designer, save
• Click on "Customize" search results layout in Designer
• Click inside the code editor: weird text in the code editor (see screenshot 1)
• Edit search results layout, click on Save: nothing happens
• Navigate to another part of Designer: I am prompted to save my changes.
• Click on "Save Changes": nothing happens

Workaround:

• Click on "Revert Changes" button, confirm, then try customizing the results page again: default layout appears as expected and I am able to modify and save the results (see screenshot 2)