Strange issue, dockerd and firewall

I am testing dockerd with success from some days now.
I am using 21.02.0 on an EspressoBin MVEBU.
All works fine, except the network access to my containers !
I have 2 on the OpenWrt host.
1 with Nginx Proxy Manager
1 other with NextCloud

After a fresh reboot, I need to wait a few minutes and make a service firewall reload before the 2 guests become accessible !...

Any clue or advice to debug this issue will be welcome.