Seems that Telekom is working on the issue. Other gaming platforms (PSN, Nintendo, Twitch) have the same issues via Telekom networks. A quick Twitter search shows a lot of complaints:
https://twitter.com/search?q=psn%20telekom&src=typed_query&f=live
https://twitter.com/search?q=telekom%20twitch&src=typed_query&f=live
https://twitter.com/search?q=telekom%20nintendo&src=typed_query&f=live