ubuntu 16.04 webmin 1.890
issue began in the early morning hours when clam apparently crapped out, according to my mail.err log. messages stopped being delivered, and began piling up in the queue. manually starting clam and flushing the queue got things rolling again. but i was perplexed as a previous reboot should have done the trick. so i rebooted again, and the problem came back - dead clam. another manual clam start and flush, and voila!
so, for the heck of it, i went to bootup and shutdown, clamav-daemon, and changed it to NOT start at boot time and saved. then i attempted to reverse it, but after setting it to start at boot time and clicking save, i get "Failed to save action : Systemd service clamav-daemon cannot be created unless a command is given".