If you have to inject / create a React Native module into your Android Activity (that does not extend the default React Native Activity), please beware that the Activity lifecycle is not tied to the React Context lifecycle used to create the RN module.
So you have to be careful to retrieve it at the right moment, bearing in mind that a developer can hot reload (pressing double R on the simulator), causing the creation of a new React Context.
Also, the framework gives you a way to listen to the lifecycle of the topmost React Native Acitivity, so that you don’t need to hold a reference to it.
To show how to solve these things, I wrote a short example that you can find here.
Here is what the running app look like: