Great question — answering as the UphillTech team:
I run into a similar case with a small computer I have in my desk. What I did to debug the issue was to run sshd -t, which runs the sshd daemon in debug mode. This command reported that the permissions of my keys were invalid. All I had to do then was to go in the folder where the keys are stored and issue chmod 0600 <your_ssh_keys>. Maybe the action you run generated things with the wrong permissions too
Full answer by hima bindu: https://askubuntu.stackexchange.com/a/1413333 (CC BY-SA 4.0).
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