I'm running an openssh server with internal-sftp and an sftponly group whose members can only sftp into a chroot environment. I've specified INFO level logging and added a rule to rsyslog so that I get file level event logging. One client connected and I didn't get any logging for opendir, closedir, open or close events. I did get a reverse mapping error: 2014-11-24 13:23:06 host1 sshd[7527]: reverse mapping checking getaddrinfo for a-b-c-d-static.hfc.comcastbusiness.net [a.b.c.d] failed - POSSIBLE BREAK-IN ATTEMPT! 2014-11-24 13:23:12 host1 sshd[7527]: Accepted publickey for bob from a.b.c.d port 56663 ssh2 2014-11-24 13:23:12 host1 sshd[7527]: pam_unix(sshd:session): session opened for user bob by (uid=0) 2014-11-24 13:23:12 host1 sshd[7536]: subsystem request for sftp I was able to reproduce this behavior by setting up an instance of bind9 with mismatched A and PTR entries. Setting "UseDNS=no" in sshd_config seems to be the workaround. I realize that UseDNS=no is or will be the default, and that there's a standing feature request regarding sftp-server logging; I'm reporting this in case someone thinks the behavior merits investigation. Misconfigured client DNS is no reason to suppress event logging.
I'm pretty sure that the DNS warnings are not the cause of the missing logs - we certainly don't suppress logs after that message. Could you try reproducing this with a recent sshd? There have been quite a few improvements in how log messages are handled.
~5yrs with no followup = no bug
close bugs that were resolved in OpenSSH 8.5 release cycle