That was a false lead after all. I will write down the solution that worked for me here - perhaps someone will stumble upon it in the future. The cause of the issue was the home assistant instance,...

OK - I've played around with it more and it seems that I've narrowed down the problem to UDP packet handling. The problem got resolved when I switched AdGuard back on and configured it to use DNS...

I've done some further testing and unfortunately nothing really helped. I've circumvented AdGuard completely to rule out that as source of the problem. I've configured the router to use default Auto...

@MR.S Thanks - I'll give it a go and see if there's any improvement in stability.

@MR.S I know that seems like the case, but what absolutely puzzles me is why only restarting the router resolves this problem. I can reboot the RPi/ADH and it does not help at all - I'm running it on...

Thank you for the answers. In the Adguard config I'm using public DNSes as upstream - I have these set up, but I've experimented with different options when I run into these issues https:// dns10 ....