I may have resolved the issue. Essentially, I started again. 
So for others, this is what I did …
I removed ClamAV …
dnf remove clamav clamav-update clamd
I removed old config files and their backups leftover from the previous ClamAV install …
/etc/clamd.d/scan.conf
/etc/freshclam.conf
I stopped Axigen …
/etc/init.d/axigen stop
I reinstalled Axigen (just to ensure it was a clean’ish install) …
dnf reinstall axigen-10.6.1-1.x86_64.rpm -y
I cleaned the dnf caches etc (maybe not necessary, but just to start fresh) …
dnf clean all
I reinstalled EPEL (again, maybe not necessary, just a refresh) …
dnf reinstall epel-release
I then reinstalled ClamAV per the Axigen KB article above …
dnf install clamav clamav-update clamd
This time every step completed without errors
And finally restarted Axigen …
/etc/init.d/axigen start
Back in WebAdmin and enabled and configured ClamAV.
I need to do some testing, but I’m quietly confident all is well.