Strange problem with companion app

Hi,

My HA setup was running perfectly then I switched Internet providers and got a new router.

I have the companion app installed on 3 phones, all android. My own, my sons and my wifes.

Mine and my wifes work perfectly just as normal.

My sons will only connect when on the home WiFi… However I have only input my external duckdns address… Not the internal one…

So why would one phone not connect when 2 do? And why will it connect to the external address but only using home WiFi?

I’m so confused… Any help on where to even start diagnosing this is greatly appreciated

Did you use trusted networks to login?

I’m sorry but I don’t even know where this setting is in the app…