I have been using Vigor routers, exclusively, since the V2200USB.

I am now upgrading from a V2700VG to a V2860Vn+.

My primary connection is adsl but I wish to use an LTE router (Huawei B593s-22) as backup. I have configured Wan2 (and the Huawei) to static IP (a private IP outside of my LAN), setting it as backup to Wan1, and this seems to be working well - if the dsl goes down, traffic starts flowing through WAN2.

However, I seem to be unable to access the Huawei Web management page while the primary connection is active - is there a configuration which will allow me to connect to the Huawei while it is not providing the active connection?

Perhaps some fiddling with a parallel LAN connection between the two routers, alongside the WAN connection, is necessary?

Not sure but i think you need to change the ip address of the hawei example if is the same as the vigor 192.168.1.1 change it to example 192.168.0.1

Maybe set a static route or route policy for the LTE connection's admin IP...but without knowing the IP configuration/topology, this might not be valid.