I had the same issue. Everything worked for a long time with dhcpcd getting its IP from my DD-WRT router, which also handled all the DNS for my lan; including handing out a "static" IP to my server. I honestly don't know what changed either. I generally don't reboot too often so many updates had happened in the interim making it unlikely I was going to be able to track down the exact change that caused the problem. The solution that worked for me, once I realised samba was failing because it wasn't getting an IP early enough, was with the Funtoo networking config assigning my IP address during boot before samba gave up and failed.
This is what I have in my /etc/conf.d/netif.eth0:
template="interface"
ipaddr="192.168.145.22"
gateway="192.168.145.1"
nameservers="...."
domain="server.me.lan"
But like you said, it might be your upgrade of OpenWRT that did it.