wp-login.php page: Cookies are blocked due to unexpected output.

Hi,

I run my school site https://www.ecolepleinair.be
PHP info: https://www.ecolepleinair.be/inho.php
Suddenly, wp-admin started to show me a blank page.
I tried wp-login.php and found

ERROR: Cookies are blocked due to unexpected output. For help, please see this documentation or try the support forums.

What I treid:

I’ve set WP_DEBUG to true and have received not errors

`define(‘WP_DEBUG’, true);
define(‘WP_DEBUG_LOG’, true);
define(‘WP_DEBUG_DISPLAY’, false);
@ini_set(‘display_errors’, 0);

I don’t see nay erorrs ?? and I don’t found log file

I renamed plugin folder to pluginold, created an empty “plugin” folder: nothing, same error with all plugins disabled

I installed “Twenty Twelve” theme and activated it: nothing changed

So plugins and theme are OK and something wring with my WP files?

-checked functions.php: nothing added (compared with a version from backup)
-ensured both functions.php and wp-config had no spaces at beginning or end of file (compared with a version from my backup using diffchecker.com)
-I compared .htaccess file with an original one (from backup): nothing added/removed.

Well, nothing found.

If you have <strong>any ideas </strong>please share them with me.
May be replace all WP files with a new from backup?

Thanks

BTW, I am still able to work in admin-wp: page is always opened on Google chrome, and I am not disconnected. But other important user who adds the content cannot login. He reported this issue and I tried to open the page with a different browser and found this blank page + “Cookies are blocked” error. So if I cn do something in wp-admin I can try.

Thanks