I believe that current DSA always runs all traffic through a single link from the switch chip to the CPU, even if the hardware has two. There is no user configuration of this internal link, you would have to modify the source code.
I would try reassigning the WAN to a different physical port (one of the LAN ports) in case there is a hardware problem with that port.
Thanks, Mike, for your reply and time. I will try that out.
However, the router is brand new, so I doubt there might be any problem with the port. I believe it is more of a configuration or hardcoding issue in OpenWRT, especially considering this has happened in similar routers with former versions of OpenWRT too.
and? are you sure those scripts/functions mentioned in the post are not used since? because strangely I can find those in release 21.02 as well.
with DSA you can configure each port to participate in any logical network construct indeed, but still the physical ports get their default names somehow. as I see there are various naming conventions used per platform/board it looks to me that convention is hw/platform specific (e.g. lanX or ethX names i've seen). thus if the question is that which physical port should be called "wan" then i think the post may still stand. but of course i can be wrong, if you know how it is exactly working please tell.
if question is only which port to be used for a construct in DSA it is easy: use list ports or option device directive with port you wish. but it will not change the name of the device, the one physical port called lan1 will be the same port regardless if you add to bridgeA or bridgeB.
and of course you can rename your ports with ip command too.