Help Needed Setting up port forwarding with Dual Wan on AC88U

[yaswan]

Hey Guys,

I'm a total noob to networking (your patience and understanding is much appreciated) and need some help getting port forwarding to work on my home network.

I'm running Merlin on an AC88U.

My network setup is as follows.
Two ISP provided routers (Huawei HG8245H [Wan Port] and a ZLT P28 [Lan1] on two separate subnets) are connected in dual Wan balanced mode to my AC88U. All the traffic, save for a couple of STB set top boxes and Netflix specific traffic, are routed via the primary Wan
The AC88U is also daisy chained via ethernet to 3 more Netgear Wifi extenders as well.
UPNP is disabled on all three routers

The Problem
I am attempting to make some servers (plex vpn etc.) available via port forwarding. Although I have enabled port forwarding on my AC88U and my primary Wan router (and also my secondary Wan router for good measure) when attempting to access the servers externally the connections time out.

Is there a particular setting I should be enabling on Merlin to get this to work?
Routing table screenshots attached

Wan 1:

Wan2:

AC88U:

Thanks in advance for any help

 

[yaswan]

Further attaching AC88U WAN settings