Since 28th December I can't install new apps and can't update my newspaper. How can this problem be solved?

I can't update my newspaper "Welt HD", nor can I install new apps from the app store.

When I try to install an app, only new Icon shows up and is showing "waiting" forever. When I tried to update my newspaper, it only shows "loading" forever.

When my iPad connects to the W-LAN, for a sudden I have IP Traffic in downstream. When I turn off my iPad, the traffic goes away.

I tried to turn off and reset my iPad several times with no result.

Many thanks for all tips,

Regards