openwrt ssh connection refused

Symptom

Normal connection attempt

$ ssh root@192.168.1.1
Connection to 192.168.1.1 closed.

End of log with verbose ssh

debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering public key: /home/z/.ssh/id_ed25519 ED25519 SHA256:XX//XX/XX agent
debug1: Server accepts key: /home/z/.ssh/id_ed25519 ED25519 SHA256:XX//XX/XX agent
Authenticated to 192.168.1.1 ([192.168.1.1]:22) using "publickey".
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: pledge: filesystem
debug1: Sending environment.
debug1: channel 0: setting env LANG = "en_US.UTF-8"
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
Connection to 192.168.1.1 closed.
Transferred: sent 2488, received 1012 bytes, in 0.0 seconds
Bytes per second: sent 346691.3, received 141017.5
debug1: Exit status 1

System log snippet in OpenWRT's luci interface

Sat May 20 23:02:33 2023 authpriv.notice dropbear[7690]: Pubkey auth succeeded for 'root' with ssh-ed25519 key SHA256:XX//XX/XX from 192.168.1.X:X
Sat May 20 23:02:33 2023 authpriv.info dropbear[7691]: Exit (root) from <192.168.1.X:X>: Child failed
Sat May 20 23:02:33 2023 authpriv.info dropbear[7690]: Exit (root) from <192.168.1.X:X>: Disconnect received

Background

A few weeks ago, I installed OpenWRT 22.03.3 on my Belkin RT3200. SSH and everything else was working fine until I updated it to OpenWRT 22.03.5, and then immedietly SSH refused to connect.

Solution

I read a GitHub conversation about a similar problem. In their case, zsh was missing, and I remembered that earlier I installed Bash. I reinstalled it via LuCI, and then SSH worked again.