> very few users are likely to be affected by this

I have a reasonably strong suspicion that I experienced this a week or two back, on a MacBook that doesn't go into sleep automatically and quite likely had 50-ish days of uptime.

It had all the symptoms described - tcp connections not working while I could still ping everywhere just fine, and all the other devices on the same network were fine. Switching WiFi networks and plugging in to ethernet didn't help. A reboot "fixed" it.