White Pages after update

Hello,

after Theme Update to Version 4.3.13 some users get only white pages after the login.

Other users can use the Site.

I deactivated all plugins with no change.

I installed Twenty Seventeen Theme and the problem is solved for all users.

How can I find out, what the Kleo problem is?

There is no log in the Browser console.

And set this config.php params has no event:

define( ‘WP_DEBUG’, true );
define( ‘WP_DEBUG_DISPLAY’, true);
define( ‘WP_DEBUG_LOG’, true );

I see neither error messages on the screen nor in the debug.log.

What can I check?

Thanks in advance!