Unifi Dream Router (UDR) shows internet offline but is online

My Unifi Dream router showed the internet status as offline since it had been upgraded to Unifi OS 3.x Per default the device tries to reach the address ping.ubnt.com which was reachable without any issues on the commandline of the device. Nevertheless i was not able to figure out why that doesn’t work. A thread on Reddit  finally told me the correct solution - it is possible to change the address....