Fixed! I downgraded from PHP 7.1 to PHP 7.0 on the server. Thanks

System Check OK:
WordPress 4.0 or later –> 4.9.5 OK
Apache or Nginx –> Apache OK
php.ini memory limit: 40MB (recommended: 96M) –> 512 OK
PHP version 5.2.4 or greater (recommended: PHP 5.4 or greater) –> 7.1.16 OK
MySQL version 5.0 or greater (recommended: MySQL 5.5 or greater) –> 5.5 OK
Mod Security OFF –> OK

Deactivating all plugins the problem remains so it is not a conflict problem.

I repeat that with the default theme (Twenty seventeen) everything works perfectly so it’s a problem introduced by the newspaper theme. As I work mainly with images, I need it to be fixed quickly. Thanks

To solve the problem I had to activate another AMP plugin. For this reason it now seems that the problem is not there but if you activate your plugin the error 404 reoccurs again. If you want to do a test disables the current test and reactivates yours. Thanks

• This reply was modified 8 years by fcaperchi.

Done! It was the fault of an external ADS. Thanks, Fabrizio

Hello. I installed the theme via FTP again. Enabled first twentyseventeen theme and then reactivated Newspaper. The posts in draft are corrected with the sidebar in its place but those already in draft are correct with the sidebar in place
published have the same problem as before and I don’t know how to solve it. I tried to disable the sidebar and reactivate it, to change the sidebar, but the result is always the same. What can I do?

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Thanks !
I hope not to lose all the changes made, however