Network issue:
Noted. Next time problem occurs I'll know for sure.
Network adapter:
QTS1081B is on the sticker
DNS Cache:
I'd looked into this and found the 1 day cache statements as well. However when on YouTube I see my Windows 10 PC checking www.youtube.com about every 6 minutes in the Pihole logs. Type A and HTTPS checks alike. Oddly Pihole rarely caches these lookups, going by the log.
The CNAME record has the day long TTL.
Its associated A records have a shorter one.
I 'm afraid that is just a relabeled RD9700.
Those cheap models are claiming 100Mbit/s line speeds, but are indeed capable of just about 10Mbit/s, as imposed by their USB 1.1 interface (max. 12MBit/s).
Running iperf3 should reveal your adapter's speed. You'd need to install that on two machines in your network for testing.
In addition, there are reports that those adaptors all come with the same MAC address.
If you'd operate more than one of those adapaters in your network, they cannot work reliably, as your router would have a hard time telling them apart.
If your adaptor turns out to be of that variety, I'd recommend to replace it for something more reliable.
It was connected to a managed switch once and I noticed 10 half-duplex which although annoying is not a problem for what I use it for. Quick speedtest and it looks still to be the case:
Download: 6.01 Mbit/s
Upload: 5.13 Mbit/s
The only reason I use a Pi Zero and not a Raspberry Pi 4 Model B is that my Pi of 7 years died during Covid lockdown and availability hasn't recovered yet. Couple of months with a bit of luck then I'll swap it out.
Thanks for your input, if you wish to close the ticket that's fine but I'll still run through these debug steps next time it dies.
We usually don't close topics, unless there would be an obvious solution.
Most often, the original topic creator would mark a post in a topic as solution. 
Independent of the above, Discourse would auto-close topics after a certain period of inactivity.
This topic was automatically closed 7 days after the last reply. New replies are no longer allowed.