For once, I have to confirm an issue which has been reported before by others on the net:
Since I upgraded my OP6 to Android Pie, I have an issue when using the phone as tethering hotspot for my work notebook by WiFi.
Apparently the DNS resolution does not work any longer despite the usual commonly known rules. At github the issue has been discussed since end of 2018 but is still unresolved. That thread mentioned UID 1052 (some strange unknown app uid) as being blocked by AFWall+, filling up the logfile with the DNS requests of my notebook. At some reddit forum I learned that UID 1052 indeed is dnsmasqd in Android Pie, so I applied some custom script, and voilà, DNS resolution suddenly works again through tethering.
Some side checks (disabling the firewall completely as well as trying "nslookup targetdomain.com 220.127.116.11" without that custom script) confirmed without any doubt that AFWall+ is the culprit here, because UID 1052 does not show up in the apps list, and in whitelist mode this results clearly in these blocking of the DNS requests from the tethering clients.
At the same time, though, DNS lookups work fine directly on the OP6 at any time.