So, installation went without a problem. Great job!
I installed the android app and pointed it to my server, according to your documentation. Went flawlessly, too.
But no data is visible in the yunohost-frontend. Looking at the looks, this could be the problem:
[26-Feb-2018 18:46:53] WARNING: [pool owntracks] child 20246 said into stderr: "NOTICE: PHP message: PHP Fatal error: Call to undefined method mysqli_stmt::get_result() in /var/www/owntracks/map_points.php on line 39"