it seems like creation of /etc/docker/daemon.json does not survive shutdown/restart cycle of the unraid server.
Of course such settings have to persist somewhere, i guess it has to be somewhere in the /boot folder (the stick)
I added 3 lines to the /boot/config/go script to create daemon.json during boot:
# Setup docker daemon.json
mkdir /etc/docker
echo {\"insecure-registries\": [\"192.168.0.54:5000\"]} > /etc/docker/daemon.json
But I guess there must be a better solution than that.