It's the Orbi invocation of SpeedTest that's generating mystery traffic!!!

Excellent question and it has triggered a thought.

Yes, it's that grafana. It's in a Home Assistant instance. It gets the data from the Traffic Meter feature of the router, which is coming from the Netgear integration with HomeAssistant. Your question made me think about that so I started digging through their docs. This bit is especially interesting, particularly the note of warning at the end of the paragraph. I know that I disabled the downlink and uplink entities long ago, but I don't remember doing anything with the ping entity. So, if that's still enabled in HA, then the integration is still running the full speed test every 2 hours. I may be taking an extended lunch break to head home and verify if any one of those 3 entities are still enabled and if so, I'll disable it and unblock access to speedtest.net. Assuming that 1) I don't see a spike in network traffic every two hours and 2) the last updated field in the Admin pages of the Router management remains unchanged, then I think we've found the culprit. It's also interesting to me that the HA integration might be updating the last run time value of the Speed Test results page in the router's management tool -- but if it's a true integration and invoking speed test as offered by the router, then it makes sense. 

If this is the issue, which won't surprise me at this point based on those docs, my frustration with lack of configuration flexibility persists, but will have moved from the Netgear product to this 3rd-party integration with the product. I'll share updates here hopefully later today when I get hands-on with it to check the state of the 3 named entities that would trigger the speed test.