That made my head hurt just reading that.Yes... seems odd that it requires a "guest" network.
Perhaps the WPA/Security is a bit different on a guest network.
I actually had a similar odd problem with 3 of my LG appliances.
After working for a couple of years, suddenly none of them would connect.
I tried all of the various suggestions... 2.4Ghz only, no special characters in the password, etc..
I ended up having to delete the app from my phone, re-adding it, and then deleting all of the appliance profiles from the app and installing them as new.
Once I did all of that, they reconnected fine.
I sell internet at my store and one thing I will warn anyone interested in getting into the internet business is that when you sell someone internet, you magically become responsible for ALL of their wifi connected devices.
I actually have had customers call and say "your internet isn't working" After a little questioning, it will turn out that every device works except ONE......well it certainly can't be that device now can it
One thing being in this business HAS taught me is how to enjoy a fine bourbon.