Recently went through many of the steps listed here, and elsewhere to configure Pihole alongside OMV5 via Docker inside a container on raspbian OS (Raspi 3b+), using a macvlan network to connect to the underlying network.
I was experiencing the same issue; unable to access the Pihole admin page until I pinged each individual client within the container console.
I had found elsewhere that using rpi-update had worked; this is how I corrected my issue.
I'm sure this causes other problems however it seems to be running well for me. I'm not yet a pro; does this indicate there was a conflict between macvlan or docker and the raspbian kernel?