That moment when you forget to run sudo ufw allow ssh after enabling the firewall

Not exactly the same thing, but on one of my systems, eth0 and eth1 swapped position after a kernel update, so the IP was on the wrong interface. I had IPMI/BMC on the system so didn't have to physically go to it and plug in a keyboard and monitor, but I still had to deal with manually typing a long randomly-generated password, twice (one to log in and once again for sudo).

I'm glad "predictable" interface names are supported now. Those eth0/eth1/etc names were dangerous since the numbers were just based on the order the kernel loaded the drivers and initialized them in, which can change across reboots. The predictable names are based on physical position in the system, so they're consistent across reboots.