I have spent hours trying to understand this to the point, I did a clean install of POP OS 19.10 to see if this resolves the issue, and no it does not.
This seems to work fine on my Mac Book, windows machine and my ubuntu server machine at home, but for some strange reason on my pop os installation internal name resolution only works for about 10 minutes after boot and then stops.
I removed the minimal dns 4 entry in the switch configs... mucked around on resolv.conf to no avail. After about ten minutes it just annoyingly stops working.
I have a mikrotik router, where I set up some static dns entries for my local environment.
The mikrotik hands all three resolver addresses out by DHCP. After digging around I had a look at the results of the
systemd-resolve --status cmd and found that occasionally the primary DNS is replaced by the secondary DNS. This seems to result in the internal resolutions to be ignored
Current DNS Server: 126.96.36.199 DNS Servers: 192.168.88.1 188.8.131.52 184.108.40.206
Appears that the mikrotik DNS lookup times out intermittently causing this issue. Upon timeout systemd-resolved switches to one of the fallback dns entries and never tries the primary again.
Not sure how to solve this one. Any help will be greatly appreciated