Validation failed error in admin panel for Complex Page Collections

Support
1

The code works correctly, but when you try to save through the admin panel, a validation error occurs. How to write it down correctly?

57
Screen Shot 2018-06-07 at 13.08.57.png1272×578 34.7 KB

header 
content:
    items: 
        - '@self.modular'
        - '@page.modular': '/action'
        - '@page.modular': '/subscribe'
        - '@page.modular': '/address'
2

What validator uses GRAV system? So I can fix the code. The site works well and I can’t find the error with online validators. The function of editing pages through the admin panel is important for the site owner. All updates are installed.
P. S. There was still an attempt to make an automatic fix code in the new version of the panel. Yes it corrects, gives save, but change the page template on the Blog instead of Modular. And when you trying to save again writes the same validation error.