Ran into something new that I thought I’d share: I have a laptop running Ubuntu Gnome (18.04 LTS) that I’d previously configured with ssh-keygen / ssh-copy-id to ssh between laptop and primary desktop. Decided to install Pop!_OS on a new partition on the laptop. After configuration, I got a MITM warning from primary when trying to ssh to laptop because EDCSA key is different. The solution was to run ssh-keyscan, copy the response info and add that to end of ~/.ssh/known_hosts and rehash known_hosts file. Commands are:
~$ ssh-keyscan -t ecdsa laptop_ip
~$ vim ~/$HOME/.ssh/known_hosts
~$ ssh-keygen -H
source for solution: https://serverfault.com/questions/321167/add-correct-host-key-in-known-hosts-multiple-ssh-host-keys-per-hostname