部分SFTP客户端认证成功后快速断开连接的异常排查求助

我管理着一台SFTP服务器，自己连接完全没问题，大部分客户端也能正常使用，但有一小部分客户端总是遇到连接故障。以下是他们反馈的客户端报错信息：

Failed to authenticate. Verify the credentials and try again. Domo is ready, but the credentials you entered are invalid. Verify your account credentials and try again. Domo is ready, but we were unable to connect to the SFTP server. Please check your settings and try again.

Permission Denied (publickey, gssapi-keyex, gssapi-with-mic). Connection Closed.

再看看服务器端的日志记录：

Oct 15 08:00:36.604 pam_unix(sshd:session): session closed for user <user>
Oct 15 08:00:34.946 pam_unix(sshd:session): session opened for user <user> (uid=1020) by (uid=0)
Oct 15 08:00:34.650 Accepted publickey for <user> from <IP> port 21191 ssh2: RSA SHA256:<hash>

从日志来看，客户端明明已经成功通过公钥认证，会话也正常打开了，但紧接着就被关闭了。可客户端那边却显示认证失败或者无法连接的提示，这实在让我摸不着头绪。有没有大佬能指点下，这种情况该从哪些方向排查问题呢？

备注：内容来源于stack exchange，提问作者Supergibbs