Why am I seeing entries in journalctl like "sshd[144488]: fatal: Timeout before authentication for 51.89.14.103 port 42396"?

Question

I'm seeing a few entries like this every day in the output of journalctl. The IP address and the port number changes.

I am trying to debug the occasional crash of this Ubuntu machine and have started following journalctl, I was not expecting to see entries like this.