Same here, re-appearing in 2.4.3-RELEASE-p1 on a Netgate SG-3100. Looks to me too high i/o(???)
PFSense installed on 'thrid party' pc hardware works normally.
Restarting ClamAV works for some hours and then protocol errors appear again.
Updating ClamAV once a day lowered to once a week -> no difference
Bypassing will prevent this ICAP protocol error but is not really a solution.
Thanks,
Imp