I think that the update process has to stop the clamd daemon. The issue is why the socket file is removed.
Check your clamav-daemon service when the system throws this error
sudo systemctl status clamav-daemon
I have found that in a Zentyal 6.1 test system there are two ClamAV sockets, the first one in /run/clamav and the other one in the old /var/run/clamav (they seem to be independent files none is symbolic link)
According to my '/etc/clamav/clamd.conf' file we are using "LocalSocket /var/run/clamav/clamd.ctl"
Could be useful check the behavior if changing the LocalSocket directive to point the /run/clamav/clamd.ctl
Any case, use strace to trace freshclam and paste here the output (or the link to pastebin)
Cheers!