Thanks for the information.
I have configured three interfaces, a WAN interface connected to my home network, a WWAN interface, also connected to my home network, and a MOB1S1A1 interface connected to an APN. I configured failover order as follows: WAN, WWAN, MOB1S1A1. Now I did some tests concerning failover.
First I disconnected WAN, the router correctly switched to WWAN, while, as you said, the indicator "MAIN" moved to WWAN. Then, in menu Network | Interfaces, I stopped WWAN to force a switch to MOB1S1A1. It worked correctly, the indicator "MAIN" also moved behind MOB1S1A1.
Second, I wanted to step up in reverse sequence. So, in menu Network | Interfaces I re-enabled WWAN; nothing happened; the router stuck on MOB1S1A1 with indicator "MAIN". I had to reboot the router to get WWAN running again. Then I re-connected WAN, the router automatically switched back to WAN while moving the "MAIN" indicator to WAN.
From my point of view there is something wrong with WWAN recovery from MOB1S1A1.
What do you mean?
Thanks and BR