@apaxi I have raised a ticket with my ISP as well, to see what they could find out. They found no issues with the connection itself but they do see some strange routing issues to Cloudflare outside their network, which could indeed affect DNS and cause bad stalls for even 10-30 seconds at times. Enough time for cache to expire on many devices and behavior to be similar to connectivity drop. It could also affect speed test in a way that it uses multiple servers to connect to and sometimes some of them didn't get resolved so it didn't actually set up connection - no errors shown, but resulting speed was much lower on my 1Gb connection. All very interesting even though surprising.

So far, MLO still behaves ok for me, so worth checking ISP DNS! It could be as stupid as that, without seemingly being connected to DNS. That also suggest that Deco doesn't have DNS caching itself, nor it servers as internal DNS, as even DHCP on auto just points my devices directly to the external DNS, whereas my previous routers were setting themselves as DNS for internal devices. This could explain why it was fine on previous router most of the time (lonmg internal DNS cache) but on Deco I've noticed these issues, especially on MLO - though thinking about it now I did see some drops now and then even on standard WiFi just much more rarely.

The DNS change didn't help... This just happened on MLO and all data streams were cut off on my Pixel 8.