Well it is comforting to know I am not alone lol. Rooted MI note 10, instead of vpn I am using local http proxy and the same is happening here too, internet is just gone but funny enough I can write messages in telegram when I can't even open a link in chrome.
Just chiming in: I also have a problem with DNS filtering with AdGuard v3.6 (1) on a Nokia 6 TA-1033 (Android 9 patch level okt 2020, build 00WW_6_19B_SP04, kernel 3.18.120-perf@2020-10-01T18:33:44).
Problem: very long waits before connect, connection time-outs, etc.
Work around: disable DNS filtering
DNS Filtering settings:
DNS Server: system default (at the moment my UBNT EdgeRouter via WiFi which forwards to Quad9 and / or my provider DNS servers depending on which (CDN-) domain)
DNS Filters enabled: AdGuard DNS Filter (last updated Jan 26)