Octavia API becomes unresponsive after reboot

I raised a bug for this, but tearing hair out so also posting here.

I install Octavia along with openstack-base using the vanilla overlay, which appears to work fine. However, if I then forcibly restart the octavia unit it seems that the WSGI component of the Octavia API then stops working. After a timeout, the client returns;

Unable to establish connection to ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))

In /var/log/apache2/octavia_error.log there are these messages;

[Tue Dec 22 11:13:38.488467 2020] [wsgi:error] [pid 3449:tid 139866935383808] [client] Timeout when reading response headers from daemon process 'octavia-api': /usr/bin/octavia-wsgi

Any similar experience here? Many thanks in advance!