First of all, I was quite unsure if I should only add a comment to this issue https://tracker.moodle.org/browse/MDL-38371 or to start a new one. As the existent issue is about activities, I decided to start a new one.
As the title already mentions the drag and drop function to move blocks is very hard to use. I tested it with an Android device and even with the in MDL-38371 mentioned QA Moodle course. I made a video which I will attach so that it's visible what happens.
I also tested it on an iPad 2. There the function works better, but the autoscrolling to one direction also happens if I touch the icon slightly to long.
It's difficult to get the correct time, the icon should be touched. There's no feedback that the dragging is enabled, that's also why I kept touching the icon which led to this strange behavior.