Hey,

I played today for the first time and noticed that its easy to play together, if everybody is synchronized via the metronome and the amount of bars. But when a change of a song comes, nobody is synchronized anymore.

I also had a delay of 10 seconds or so with hearing the other player. And we were even in the same city.

Is that normal?

Yes. jammr is live but not real-time. It is designed for improvising to a chord progression. The changes you can make to the chord progression without causing “collisions” are limited, so it's not suitable for performing or rehearsing entire songs in one go.

Here is a guide on how to jam successfully: https://forum.jammr.net/topic/1724/
And here is a deeper explanation of the interval-based jamming system: https://forum.jammr.net/topic/1719/