[Gelöst] Site crashes after initial WPML setup

Background of the issue:
I have just set up a brand new WP site twice and each time after the WPML setup, when I click Languages, I get this critical site error. Site URL: versteckter Link. PHP Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, cannot access private method WPML_TM_ICL20_Migration_Notices::build_migration_required() in /var/www/dev.casaboavista.com/htdocs/wp-includes/class-wp-hook.php:324 Stack trace: #0 /var/www/dev.casaboavista.com/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters() #1 /var/www/dev.casaboavista.com/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action() #2 /var/www/dev.casaboavista.com/htdocs/wp-settings.php(704): do_action() #3 /var/www/dev.casaboavista.com/wp-config.php(150): require_once('...') #4 /var/www/dev.casaboavista.com/htdocs/wp-load.php(55): require_once('...') #5 /var/www/dev.casaboavista.com/htdocs/wp-admin/admin.php(34): require_once('...') #6 {main} thrown in /var/www/dev.casaboavista.com/htdocs/wp-includes/class-wp-hook.php on line 324.

Symptoms:
Site crashes with a critical error after WPML setup when clicking on Languages.

Questions:
Why does the site crash after WPML setup?
How can I fix the critical error related to WPML?