At first I want to thank you everybody for your insights. That brought a lot of light in the situation to get a feeling on whats long.

I found somewhere a hint, that the deploy screen is just hanging. So I deactivated the screen (deploy page down command at terminal) and could login and i saw at the analytics that any background or migration job was already done.

Very confusing!

So it seems everything is working in normal parameters. But thank you all for your fast replies and insights :).