Ok, I see.
The lists of dropped objects are buggy. Including the scrollers (arrow) when the list overload in size.
It was difficult to write this and even today, this part of the soft is an ugly code. I should rewrite all this part.
To solve this issue, just move the lateral separator (with a grey circle in the middle) Move to the right, or to the left, and the objects are refreshed.
This solves also the graphical bug with partially hidden tasks in the toolbar brick.
Please always mention when you have graphical bugs.
You can refresh your page when you want when you get a such "gremlins" (like you say in joomla.org ... I like this term).
Regards.
Thank you for using Cook.