Both port specific firewall rules, and web-server IP permissions are important.

For example, bandwidth rate-limiting may be inhibited for admin SSH or package updates, and LAN IPv4 private ranges for your host address pool are set.

Finally, your internal DHCP should statically bind your admin computer MAC to a fixed LAN host IP to further reduce issues.

Personally, I always build my NAS from scratch, as I have lost count of the number of problems web-GUI have caused over the years. =3