My two cents worth.
I have all my firewalls with ClamAV, SquidClamAV and transparent web proxy.
My firewalls scheduled to reboot regularly to minimise any memory leakage issues etc.
I noticed a year or so ago that web proxy service and sometimes ClamAV service not started after a reboot.
I disabled web proxy and SquidClamAV and ClamAV, uninstalled from pakfire, reinstalled and re-enabled clam/clamav/proxy.
On most of the firewalls, this fixed the problem, however I have a few remaining where startup fails on reboot. The firewalls that are all failing have HDD, the working ones have SSD.
My thoughts are that there is a timing issue with the slower HDD based ones.
I even recently did a backup, fresh install and restore (not squid/squidclamav data) and still failed on HDD based firewall.