Wired network fails after a while on the Pi 4

Symptoms:
The Pi seemingly freezes up after about an hour (time varies), requiring hard reset.

Reality:
dhcpcd crashed/froze and didn't restart, and the network config got removed from the interface.
System can temporarily be recovered by statically assigning ip & route, or by running systemctl restart dhcpcd in a serial terminal or with a directly connected keyboard and mouse.

Workaround:
Add the following to /etc/dhcpcd.conf:

# https://github.com/raspberrypi/linux/issues/4092/
denyinterfaces veth*

Raspberry Pi 4: DHCPCD route socket overflowed

Also tracked by Jeff Geerling: Pi drops IPv4 address after DHCP lease expires