Cannot load prebuilt layouts

Same as https://siteorigin.com/thread/page-builder-not-loading-pre-built-layouts/

When I try to insert a prebuilt layout (any of them), the dialog displays a clocking indicator with ‘Loading prebuilt layout’. It never times out or loads.

If I close the ‘Page Builder Layouts’ dialog and reopen it, the status area still says ‘Loading prebuilt layout’, but without the animation.

I need to deactivate and re-activate PageBuilder in order for the message to disappear.

To iterate, at no time does the layout load.