Yesterday and today I have worked from home rather than going into the office.
Both days my internet connection has become unusably slow sometime in the afternoon. This has happened before: I used to joke that it happened "When the kids got home from school." But the kids are still on summer vacation. Still, it could be "When the kids get off from day camp", or "When the stockbroker down the street stops trading for the day".
This afternoon slowness has happened many times before - so much so that I fell into the habit of driving into the office rather than working from home. I had forgotten that this was the reason I was not working from home - I was wondering why I was not using my treadmill desk, which I love, as much as I would like (because I prefer to read email in the afternoon on my treadmill desk - and if my Comcast internet is unusably slow, then I try to be in the office in the afternoon, and hence do not use my treadmill desk).
I have not hitherto investigated this problem in detail. Apart from saying "This is probably bufferbloat", but never getting around to installing modern OpenWRT, with bufferbloat mitigation, on my routers (because my first attempts to install CeroWRT/OpenWRT/DDWRT failed, possibly locked routers).
This blog item to hold notes related to investigating this problem. In public, because it is unlikely to hurt, may embarrass Comcast into fixing the problem, etc.