NextDNS slows down by Ubuntu checking apt repositories for updates

This is really weird. I have NextDNS running on my router. it works really well.

I have two Ubuntu boxes on the network. When I just use it this way (unmodified Ubuntu network settings), everything is fine throughput wise.

However when I change my ubuntu settings to NextDNS so Ican use DOH and also see named requests on NextDNS analytics, whenever I sudo apt update it goes very very slowly, but everything else internet wise (speedtest, browsing from that ubuntu box) is perfectly fine.

this happens whether I modify systemd-resolved or use the NextDNS Command-Line Client.

Any ideas? It's more an annoyance than anything else.

I have the same setup on my windows computer -- using NextDNS on the computer itself behind a nextdns router -- without slowing anything down.