The very odd situation in which I saw those buffer overflows, is simply
on a home machine, so flaky home broadband, running a pkg_rolling-replace.
The machine has 32G of memory, but from your message that is irrelevant.
The urtwmn0 was struggling (that's new BTW) and I kept having to
/etc/rc.d/wpa_supplicant restart. While texlive was being downloaded,
I hit ctrl-C, and then saw the reams of buffer messages. In terms of
routing, there is just 1 default route. Maybe all the wpa_supplicant
restarts and dhcpcd kicking in helped? (Doesn't really fit the picture...)