This is a known effect on newer Linux systems.
The kernel uses a port range for DNS-Lookups which falls in the restricted port range when using the 'Auto' setting of MiamiDX internal Firewall.
To avoid this problem just enter the following on your AmigaOne as user root:
$> echo >/proc/sys/net/ipv4/ip_local_port_range 1024 5000
This instructs the Kernel to use the port range 1024-5000 which is automatically managed by MiamiDX, so your DNS Lookups are then working fine again.
You can of course set other Port ranges like i.e. 10000 - 15000 but remember to enable this range also in MiamiDX Firewall rules!