moetiker

I found the problem. In the file all-in-one-wp-migration.php

there is the setting:

// Check SSL Mode
if ( isset( $_SERVER['HTTP_X_FORWARDED_PROTO'] ) && ( $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https' ) ) {
        $_SERVER['HTTPS'] = 'on';
}

without that setting my site is looping from HTTP to HTTPS I was not aware of that because the plugin was always installed, after deactivation I had to set this by myself… I added the lines to the wp-config.php file and all was back to normal.