Trying to use notifications to return to my App, I found that when clicking the notification message Another Activity Instance was launched.

The way this was solved (I needed to return to the opened instance) was to add to the Activity tag in the AndroidManifest.xml the folowing code:
android:launchMode = "singleInstance"

example:

<activity android:name="MyActivity" android:launchMode = "singleInstance" android:configChanges="orientation"
android:label="@string/app_name">