What are the possible reasons for an android app failing to receive BLE notifications from a BLE device it's connected to?

Question

I have posted several questions which are basically the same question over and over again because I honestly can't find the problem.

I need to receive notifications from a BLE device on a particular characteristic. I use the BGX Silicon Labs Bluetooth kit which is connected to a Processor board that we send and receive data from. The documentation states that two characteristics RX and TX are used for data exchange. Rx for sending and TX for receiving.

Here is the link as well:https://docs.silabs.com/gecko-os/1/bgx/latest/ble-services

Now I tried following the guide from PunchThrough that helps build a starter BLE app for android. I pretty much did everything they did. Now when I enable notifications for the RX characteristic when sending, the onCharacteristicChanged override function gets called as it should be. But when I send a request using that characteristic and expect a response based on that request sent in the form of a notification. Our team seems to manage fine using the software developed for the Desktop version, the android version I am working on however seems to succeed only in Writing data but not receiving. My question is simple, why does the onCharacteristicChanged function never get called when I enable notifications on the Tx characteristic?

The code has a queuing mechanism, and it writes to the descriptor and has notifications enabled on the TX characteristic but I get nothing, nothing at all. I can provide parts of the code if you wish but first I wanted to discuss what possible reason notifications are not received.