Android disconnects automatically from WiFi without internet below Android 10

The problem you mentioned might not be because of the code you provided at Issuetracker. Once i fixed the problem in my device (Android 9), i am unable to replicate the error even after a complete undo. I even tried device reboot, app reinstallation or even factory reset. Try this.

1. In Setting --> Apps & Permissions, the test app requests for a Location permission. Give it the permisson.

2. Java code can be

   private void connectToWiFi(final String ssid, String password) {
   
   if (connectivityManager != null) {
   
       try {
           connectivityManager.bindProcessToNetwork(null);
           connectivityManager.unregisterNetworkCallback(networkCallback);
       } catch (Exception e) {
           Log.d(TAG, "Connectivity Manager is already unregistered");
       }
   }
   
   NetworkRequest.Builder request = new NetworkRequest.Builder();
   request.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
   if(isOnline()==false){
       request.removeCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
   }
   
   networkCallback = new ConnectivityManager.NetworkCallback() {
   
       @Override
       public void onAvailable(Network network) {
   
           String networkSSID = getNetworkSsid();
           Log.e(TAG, "Network is available - " + networkSSID);
   
           if (networkSSID.equals(ssid)) {
               if(isOnline()==false){
                   Log.e(TAG, "bindProcessToNetwork");
                   connectivityManager.bindProcessToNetwork(network);
               }
           }
       }
   
       @Override
       public void onUnavailable() {
           super.onUnavailable();
           Log.e(TAG, "Network is Unavailable");
       }
   
       @Override
       public void onLost(@NonNull Network network) {
           super.onLost(network);
           Log.e(TAG, "Lost Network Connection");
       }
   };
   
   connectivityManager.registerNetworkCallback(request.build(), networkCallback);
   
   if (!wifiManager.isWifiEnabled()) {
       wifiManager.setWifiEnabled(true);
   }
   
   WifiConfiguration config = new WifiConfiguration();
   config.SSID = String.format("\"%s\"", ssid);
   config.status = WifiConfiguration.Status.ENABLED;
   
   int netId = -1;
   List<WifiConfiguration> apList = wifiManager.getConfiguredNetworks();
   Log.d(TAG, "List Size : " + apList.size());
   
   for (WifiConfiguration i : apList) {
   
       if (i.SSID != null && i.SSID.equals("\"" + ssid + "\"")) {
           netId = i.networkId;
       }
   }
   
   // Add network in Saves network list if it is not available in list
   if (netId == -1) {
   
       if (TextUtils.isEmpty(password)) {
           Log.e(TAG, "====== Connect to open network");
           config.allowedKeyManagement.set(WifiConfiguration.KeyMgmt.NONE);
       } else {
           Log.e(TAG, "====== Connect to secure network");
           config.preSharedKey = String.format("\"%s\"", password);
       }
   
       netId = wifiManager.addNetwork(config);
   }
   
   Log.d(TAG, "Connect to network : " + netId);
   wifiManager.enableNetwork(netId, true);
   
   }
   
   public boolean isOnline() {
   Runtime runtime = Runtime.getRuntime();
   try {
       Process ipProcess = runtime.exec("/system/bin/ping -c 1 8.8.8.8");
       int     exitValue = ipProcess.waitFor();
       return (exitValue == 0);
   }
   catch (IOException e)          { e.printStackTrace(); }
   catch (InterruptedException e) { e.printStackTrace(); }
   
   return false;
   }
   

If you are targeting to use your code in specific networks then you can go to yours access point interface and simply set the DHCP settings to static and give the devices an appropriate IP.

More info can be found here

Now if you are targeting networks that does you cannot access their DHCP settings, based on that link you can tell your device to stay connected to the network no matter if it has internet connection.

NetworkRequest.Builder builder;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    builder = new NetworkRequest.Builder();
    //set the transport type do WIFI
    builder.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
    connectivityManager.requestNetwork(builder.build(), new
                                 ConnectivityManager.NetworkCallback() {
        @Override
        public void onAvailable(Network network) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                if (Build.VERSION.RELEASE.equalsIgnoreCase("6.0")) {
                    if (!Settings.System.canWrite(mActivity)) {
                        Intent goToSettings = new  Intent(Settings.ACTION_MANAGE_WRITE_SETTINGS);
                        goToSettings.setData(Uri.parse("package:" + 
                        mActivity.getPackageName()));
                        mActivity.startActivity(goToSettings);
                    }
                }
                connectivityManager.bindProcessToNetwork(null);
                if (mSsid.contains("my_iot_device-xxxxxxxxx"))
                    connectivityManager.bindProcessToNetwork(network);
                else {
                    //This method was deprecated in API level 23
                    ConnectivityManager.setProcessDefaultNetwork(null);
                    if (mSsid.contains("my_iot_device-xxxxxxxxx"))
                        ConnectivityManager.setProcessDefaultNetwork(network);
                }
                connectivityManager.unregisterNetworkCallback(this);
            }
        }
    });
}

Also sometimes it is good to keep your wifi radio awake, so you gonna need to hold it using WiFiLock.

//Create a wifi manager instance first
WifiManager mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
//and then create your wifiLock
WifiManager.WifiLock mWifiLock = mWifiManager.createWifiLock(WifiManager.WIFI_MODE_FULL, "wifiLock");
if(!mWifiLock.isHeld())
        mWifiLock.acquire();

Later if you want to realese it

if(mWifiLock.isHeld())
        mWifiLock.release();

This code helped me to stay connected to my network even if it not has internet access.