Could you try and set the global setting captive_portal_detection_enabled to 0 (false).
What’s actually happening is that by default, everytime you connect to a wifi, the FW will test against a server (typically google) to see if it’s a captive wifi (needs login). So if your wifi is not connected to google, this check will fail. After that, the device knows that wifi has no internet connection and simply will not autoconnect to it.
Setting this setting to 0, will avoid this check.
Settings.Global.putInt(getContentResolver(), Settings.Global.CAPTIVE_PORTAL_DETECTION_ENABLED, 0);
You can do it through adb for testing purposes:
adb shell settings put global captive_portal_detection_enabled 0
And retrieve it’s value like this:
adb shell settings list global | grep "captive"
IMHO this is not very nice thing to do, since you are changing a setting for the user and many FWs don’t provide even an advanced setting to enable/disable this by the user itself. (Google doesn’t). But maybe it suits your needs.
Hope it helps!