And I just had it the other way around. I also have two networks. The 5GHz networks seem to show up a bit later, so the FP2 connects to the 2.4GHz first. I got the exclamation mark. Then I switched to 5GHz and the mark disappeared. So I decided to forget the 2.4GHz connection, thinking that'd be the issue. After 10 minutes my phone randomly lost WiFi connection to the 5GHz. I cycled Wifi and when it connected again it still had the exclamation mark. I cycled flight mode and it still shows the exclamation mark. Now when I check on my Wifi, the 5GHz connection disappeared. Only after 10-15seconds it shows up and the phone tries to connect again. But the 5GHz connection still disappears every now and then.
EDIT: Also, even though I set up a static address for my phone (a different one for the 5GHz and the 2.4Ghz network, I still get the exclamation mark. sometimes for one network, sometimes for the other. as soon as I switch to the other network, it's fine.