As I can see, clamav is indeed loading definitions, but does not run, and does not bind. Mail gets deferred, as postfix can't talk to it.
Disabling AV and reloading Postfix does not trigger mail flow, postfix continues to try to relay to clamav -
afaik, this is a postfix issue/feature.
FYI, my issue occurs in 5.0 beta 3