Are your phones android? On android you usually get a message when connecting to a SSID that doesn't have internet access, it states something like "no internet access, stay connected?" If you don't give an answer to the question then your phone could revert to using mobile data hence no access to the glinet gui.
When connecting to the SSID with no current WAN access, load up your phone browser and try navigate to a web URL, you might need to disable your mobile data to force the WiFi connection. When visiting a URL with no WAN you should then get the message about being no internet available, click on the stay connected option and I believe you can also remember the option too.
If you are not getting the message then just try forgetting the wireless network and connect again, you should eventually get the warning message.
Your phone may also have additional WiFi settings like in this post
My guess is it's related to this issue.