Comment 17 for bug 2017886

I was going to say that you have an extra ip rule that could be interfering with the ovn-bgp-agent ones:
304: from all iif br-ex lookup 10000 proto zebra

But it seems you have pass that point already

Yep, if host IPs are exposed, then IPs are added to bgp-nic, but if subnets are exposed, then no IP gets added to bgp-nic, but redistribute kernel but route at br-ex routing table are used.

On the first case (host IP), the network is not advertise, so if you have a virtual IP it will only be advertised in the node/vm that gets to be the chassis of the virtual port. There was a patch in neutron to update the information about those virtual IPs, perhaps you are missing it? this on ovn-bgp-agent side: https://review.opendev.org/c/openstack/ovn-bgp-agent/+/883187, and this the patch on neutron:
https://review.opendev.org/c/openstack/neutron/+/882705