H5P and Moodle 3.5.4+ installation trouble

Hi there,

i try to integrate the H5P-plugin in my moodle (moodle 3.5.4+, php7.2, ubuntu 18.04) environment but it doesn´t work. 

The appempt to run a true/false question ends in an exception-error (see attachment for more moodle debug info) "Call to a member function get_content() on boolean".

The required modules (zip, mbsting, ssl) seem to be installed on my system (see here: https://hnk.myqnapcloud.com/phpinfo.php ) and the max upload size and the max post size is comfortably set to 2048M.

My browsers are FireFox 64.02 and Chrome  71.0.3578.98.

Do you have an idea?

Thanx,

axl