Networking not started at boot after upgrade from 3.18.4 to 3.18.5

I already fixed this but I'm opening this just to document an issue I had yesterday which I can't explain but maybe somebody else can?

I have a VM at a hosting provider that I've never had any upgrade issues with, eg. apk upgrade --available. Yesterday I was working on troubleshooting something else and decided to go from 3.18.4 to 3.18.5 and when I did I couldn't ssh to the VM after reboot. I got a virtual console through the hosting provider dashboard, logged in and saw that eth0 wasn't configured, the networking service didn't appear in rc-update, and there wasn't a networking file at all under /etc/init.d.

I did an apk fix openrc, rebooted and then all was well again.

Any ideas what went wrong?