Contact Energy recently rolled out an update - https://contact.co.nz/broadband-system-update - they said it'd take a minute and we may not notice it, but it went down and stayed down for almost 2 hours before we called up and they told us to hard-reset the router.

Since then all of the devices in our house (2 laptops, 2 PCs, chromecast, 2 phones) have been struggling with connections.  There's often, but not always, a significant 5-10+ second delay before a connection is made... but then the data transfer super fast.  For example a speed test can take ages to start, but once it does, it'll push 100mbit up / 20 down no problem.  Some connections are fast (eg. loading music.youtube.com) but then requests made within the page (eg album pictures) are what lag.  To add some confusion I had massive lag on one google meet but no issues on another.  We've power cycled all the things.

To me this indicates a DNS issue.  I plugged in cloudflare's 1.1.1.1 DNS and it's a lot better but not perfect.  I grabbed wireshark to inspect the traffic but realised I have nfi what I'm doing.  However it showed quite a few connections to ipv6 addresses, so I added an ipv6 DNS too and early results seem promising.  However DNS caching is a thing which muddies the waters.  

I will give Contact a call but at this point I suspect all they'd do is tell me to hard reset the router, so I'd like to get in contact with them with some kind of solid evidence that there's something wrong with XYZ.  The problem is that all I have currently is "it takes ages to connect sometimes but then it's fine once it does connect".  Speed tests, ping tests etc don't seem to show any issues.  Charles proxy doesn't even seem to complain about some timings.  I'm too unfamiliar with Wireshark to know what I'm doing. 

Anyone have any ideas of how I can definitively (and reproducibly) log errors in a round trip connection?