If you connect to an Access Point that is not on the internet, Android will warn you or disconnect the connection. Some versions of Android have options to work around this. Sometimes there is a setting to forcibly connect a Wifi access point even when the AP does not have internet access, or an option like “Avoid poor connection”. After unchecking the option, the Android device will ignore the connection quality. Some versions of Android displayed the option as “Keep connection alive”.
ReticleOS does not have any of these options in the Settings UI, but at least in the Marshmallow derivative of ReticleOS (V4.2.x) you should see a notification after connecting to the AP with no internet access, and if you pull down that notification and select it, you should be prompted to maintain the connection. You can check the box that says always allow on this particular AP:
The bad news is that the R-7 won't automatically re-connect to the device if it disconnects. You have to manually reconnect (at least sometimes :-( ).
Also note an Application itself can workaround the problem by connecting to Wifi and using android.permission.ACCESS_WIFI_STATE, and the WifiManager (setWifiEnabled() and enableNetwork()).