Accessing separate modem which is in bridge mode via LAN

I have a 2-device setup: BT Home Hub 5A with external modem (Zyxel VMG3925-B10B)

Modem's IP address:
Router's IP address:

I have read several post on how to access the modem via a device that is connected in the OpenWrt router and I have followed exactly the proposed solution:
I did create the interface with static IP on eth0.2, etc. and I am probably ok with that.

pppoe-wan is also on eth0.2 in case this affects anything..

However, what is weird is that I can access both modem's and router's interface via a wireless device (i.e. my iPhone), but I cannot access only the modem's interface via a computer connected to OpenWRT's LAN.
To see if this is software-related, I disabled the firewall of my PC, cleaned up all history in 3 different web browsers and still nothing.

Any idea if there is anything missing in the openwrt setup that could cause this weird behaviour?

Post the output to redacting the private parts:

uci show network; uci show wireless; uci show dhcp; uci show firewall; \
ip address show; ip route show table all; ip rule show; iptables-save