We don't get any results from breitbandmessung. de if proxies for http/https are active, even if gateway av, webblocker and APT blocker are not activated.
Which settings could be the cause of this issue.
-Do you see any errors in your traffic monitor?
-Are you able to access https://www.breitbandmessung.de/ via a packet filter?
-That site appears to resolve to only 220.127.116.11 -- do you see any return traffic if you use a tool like TCPDUMP on the firewall? If you're not seeing a response, the issue may be upstream from your firewall.
See for TCPDUMP:https://www.watchguard.com/help/docs/help-center/en-US/Content/en-US/Fireware/fsm/log_message_learn_more_wsm.html
You can use an advanced argument like
"-i eth0 host 18.104.22.168 and (port 80 or port 443 or icmp)" to filter for that traffic.
WatchGuard Customer Support