Thanks everyone for the solutions - I have MWAN working again based on @fnord’s input. Also added @askingUser’s contribution in case that helped my remaining problem, but I’m not “at the end of the tunnel” yet.
As seen in the first pic taken from the Status / Overview page in LuCI, of my 4 interfaces, the two that I have enabled are online. Confirmed this by accessing the web successfully via the Omnia.
Despite trying the various suggestions, though, I don’t have full MWAN functionality. When I invoke any of Interface, Detail or Trouble Shooting under Status / Load Balancing, the page hangs indefinitely as seen in the second pic.
Oddly, at some points earlier in working on this (I think before I added @askingUser’s tweak, but I am not sure - and I’ve rebooted and fiddled a bit since first spotting this hang), the hang was NOT indefinite. It would stop after a minute or so with a message like “No MWAN Interfaces found”.
Note that Status / Load Balancing / Diagnostics also appears to hang, but the message is “Waiting for command to complete.” As I saw something like that in a prior version of MWAN3 with some of the Diagnostics actions, I’m setting this symptom aside for the moment. Probably same cause but maybe not.
Any suggestion as to what might be causing this hang?