Hi,
Sadly I can confirm this problem still persists in 2.31-13 too. I found it (before I found this report of it) yesterday upgrading a fully up to date buster vm to bullseye ... In my case I noticed it at the first conffile prompt when trying to ssh a new connection into the vm failed, which was after the first prompting from libc to restart services (and ssh was not included in the list of services to restart then). I can confirm that manually restarting ssh (while the upgrade was still in progress) did fix it to enable logins again. The interesting bit of the upgrade log is included below - I'm not sure offhand exactly how the libc restart logic is coded, but at first blush I'd note the new openssh-server is unpacked but not set up at the time the libc service restart takes place ... Cheers, Ron Unpacking openssh-sftp-server (1:8.4p1-5) over (1:7.9p1-10+deb10u2) ... Preparing to unpack .../openssh-client_1%3a8.4p1-5_amd64.deb ... Unpacking openssh-client (1:8.4p1-5) over (1:7.9p1-10+deb10u2) ... Preparing to unpack .../runit-helper_2.10.3_all.deb ... Unpacking runit-helper (2.10.3) ... Preparing to unpack .../openssh-server_1%3a8.4p1-5_amd64.deb ... Unpacking openssh-server (1:8.4p1-5) over (1:7.9p1-10+deb10u2) ... Preparing to unpack .../libc6_2.31-13_amd64.deb ... Checking for services that may need to be restarted... Checking init scripts... Unpacking libc6:amd64 (2.31-13) over (2.28-10) ... Setting up libc6:amd64 (2.31-13) ... Checking for services that may need to be restarted... Checking init scripts... Services to restart for GNU libc library upgrade: cron atd Restarting services possibly affected by the upgrade: cron: restarting...done. atd: restarting...done. Services restarted successfully. Preparing to unpack .../libc-bin_2.31-13_amd64.deb ... Unpacking libc-bin (2.31-13) over (2.28-10) ... Setting up libc-bin (2.31-13) ... ... <much later> ... Setting up openssh-server (1:8.4p1-5) ...