Problem without Jetpack.

Hi, I keep having problems with my site, without using Jetpack. With Jetpack it works normally.

The query:

http://www.gattezzadifoligno.it/wp-json

returns a correct response but the shortcode does not return any posts, not even from the site itself:

https://www.gattezzadifoligno.it/pagina-di-test

On other sites I manage, also without using Jetpack, this does not happen.
I can’t figure out where the problem is.

Thank you.

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