git errors

Error on `git pull`: Permission denied (publickey). fatal: The remote end hung up unexpectedly

Sometimes my Devuan unexpectedly close the session, because of some JavaScripts on websites. After re-login I cannot connect to remote git repository with errors:

$ ssh remote_server
$ git pull
Error reading response length from authentication socket.
Permission denied (publickey).
fatal: The remote end hung up unexpectedly

Some people advise to start ssh-agent and load keys to ssh-agent, but that does not work in my case: