I have done what you said… but I am not sure what information you need.
I recorded what the browser did when I predded the button “Bulletin” to access to the templates. Now it gives a different error: number 200.
The developer console showed three files that I share with you:
Ajax files
And in the second file i got an error message saying:
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 3696879 bytes) in /var/www/vhosts/cursilloscristiandad.archimadrid.com/httpdocs/wp-includes/functions.php on line 2999