@jackbrewster ok so let's start with something a little less intimidating. Use a wired PC in preference. We're poking around for a bunch of things:

- dropped packets
- duplicated packets
- size mismatches
- buffering problems

We can capture a lot of this information with wireshark, and then stop it and review the data.

Many issues simply show up in wireshark usually as red or black highlighted lines after capture.

Wireshark also has a menu item Analyse > Expert Information that summarises common problems for us.

The final buffering problems are often called "buffer bloat" see the 3rd link for an excellent explanation.

Try the simple browser-based testing link below. If that comes up with a C or D this is probably the root cause of the flakey performance. You can try looking into Ubiquiti Smart Queues, and reading up about Cake and CoDeL. After tuning my system internet worked a lot better, going from a C to A+, and most importantly, stable internet performance when people are doing video calls and playing games while I try to do "legit work".

It may also be possible to configure this on your xfinity modem too, you'd need to ask your ISP about that.

wireshark: https://www.wireshark.org/learn & https://www.youtube.com/@WireSharkFest or https://wireshark.com/how-to-use-wireshark/ esp section 7.2
bufferbloat: https://dgroshev.com/blog/bufferbloat/
testing: https://www.waveform.com/tools/bufferbloat
unifi smart queues: https://www.unihosted.com/blog/the-ultimate-guide-to-setting-up-unifi-smart-queues