If there isn't an update available or if the update doesn't fix the issue, you can manually patch the library by updating how AppState listeners are added and removed.

Steps to Manually Patch the Library:
Locate the node_modules/react-native-countdown-component/index.js file.
Find instances of AppState.addEventListener and AppState.removeEventListener.
Replace them with the updated API as follows:

Replace:
AppState.addEventListener('change', this._handleAppStateChange);

with:
this.appStateSubscription = AppState.addEventListener('change', this._handleAppStateChange);

Also Replace:
AppState.removeEventListener('change', this._handleAppStateChange);

with:
this.appStateSubscription && this.appStateSubscription.remove();

Save the file and re-run your project.