Fatal error after updating to 1.2.4

After updating to the latest version, the WP Admin becomes inaccessible with the following details in the error log:

PHP Fatal error:  Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, class "CMB2_Hookup" not found in /home/site/wp-includes/class-wp-hook.php:307
Stack trace:
#0 /home/site/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters('', Array)
#1 /home/site/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#2 /home/site/wp-content/plugins/learndash-topic-progression-using-storyline-or-captivate/CMB2/bootstrap.php(75): do_action('cmb2_init_hooku...', Object(CMB2))
#3 /home/site/wp-content/plugins/learndash-topic-progression-using-storyline-or-captivate/CMB2/init.php(165): cmb2_bootstrap()
#4 /home/site/wp-includes/class-wp-hook.php(307): CMB2_Bootstrap_2100_Develop->include_cmb('')
#5 /home/site/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#6 /home/site/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#7 /home/site/wp-settings.php(598): do_action('init')
#8 /home/site/wp-config.php(91): require_once('/home/site...')
#9 /home/site/wp-load.php(50): require_once('/home/site...')
#10 /home/site/wp-admin/admin.php(34): require_once('/home/site...')
#11 /home/site/wp-admin/index.php(10): require_once('/home/site...')
#12 {main}
  thrown in /home/site/wp-includes/class-wp-hook.php on line 307

Downgrading to version 1.2.3 resolves this.