Ok we did find the answer for this question:
Open week.php (in the template file) and look for the code
left: <?php echo $indent * 8 ?>px;
The 8 is the 8px left and because it is just 8px you can not see the event behind it. We changed it to 30 so:
left: <?php echo $indent * 30 ?>px;
Now we can see the other event