Dear Blizzard!
I found an error in the Blizzard App. For future patches, if you use mouseover to view their download status (while they are being downloaded), the speed of the download is not shown correctly by the client.
For me, it always wrote 0 b/s when it was downloading with more than 20 Mb/s
Due to forum rules, I could not send screenshots, but can provide them if necessary!
Thanks for the help!