However, after some time has passed, no new text will show up on the Serial Monitor.
"Some time"?
Sometimes it goes as far as i = 60, sometimes it stops just after Sometimes it goes as far as i = 60, sometimes it stops just after "Betriebsbereit."..
From when you first open Serial Monitor, the only thing displayed is "Betriebsbereit."? Just a single line of text?
Board?