USG Flex 200 DNS cache poisoning?

Hello,

Our USG Flex 200 is working just fine for clients. The device itself will not connect to the internet however. I cannot search for updates and timesync does not work for example. Using SSH to check on the machine locally the following happens:

Router> ping gmail.com

PING gmail.com (192.168.50.41) 56(84) bytes of data.

--- gmail.com ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2003ms

Strangely, when flushing the DNS cache and querying again straight afterwards:

Router> ip dns server cache-flush
server reload successful
Router> ping gmail.com
PING gmail.com (142.250.179.197) 56(84) bytes of data.
64 bytes from 142.250.179.197: icmp_seq=1 ttl=118 time=15.0 ms
64 bytes from 142.250.179.197: icmp_seq=2 ttl=118 time=14.5 ms
64 bytes from 142.250.179.197: icmp_seq=3 ttl=118 time=13.7 ms

--- gmail.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 13.788/14.459/15.041/0.533 ms

Waiting a few minutes after this and trying again:

Router> ping gmail.com
PING gmail.com (192.168.50.41) 56(84) bytes of data.

--- gmail.com ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2008ms

Machine has been rebooted, runs firmware V5.38(ABUI.0). DNS forwarders are to our ISP but changing those to 8.8.8.8 for example shows the same behaviour. We do not use the 192.168.50.x subnet, never have and never will.