Let me be clear. Perhaps we need to see your /etc/config/wireless.
I'm trying to ensure that you don't have the LAN and WAN on the same band (it seems they're both on 5.4 GHz from your descriptions). If so, the LAN SSID will always go down while WAN SSID is disconnected/reconnected. If this is the case, it would be normal behavior - as the WiFi chip needs to know the channel of the upstream WAN connection before it can establish a client AP for LAN on the same channel.
Also, if a DFS channel is being used on the upstream router, the channel may be changing. I notice none of your posts note the channel. 
If it's a non-DFS channel problem...the Travelmate package is known to help with issues like this.
EDIT: Lastly I think the logged errors you expect to find may be in the upstream router (if any exist).