strange back button behavior - my app closes instead of popping back-stack

Question

In my app I have 3 activities (I have more but lets stick with 3 for simplicity), lets call them A B and C where A is the main activity.

Activities B and C could be accessed multiple times from various locations in my app so in order not to overload the back stack and get outOfMemoryException, I launch these activities using the flag FLAG_ACTIVITY_REORDER_TO_FRONT.

However recently I started to experience some strange behavior from the back stack/back button where the back button closes the app instead of popping the top activity.

Here is an example of what is happening:

1. user open app - back stack is "A"
2. user opens activity B - back stack is "A B"
3. user opens activity C - back stack is "A B C"
4. user opens (not pressing back button) activity B again - back stack is "A C B"
5. user presses back button

Expected behavior: back stack should be "A C" and activity C should be visible on the screen again.

Actual behavior: app closes.

I have confirmed the state of the back stack with adb shell dumpsys activity and before pressing the back button the stack indeed looks like "A C B".

Any ideas why this is happening and how I can fix this?

edit

my device is LG V30 and running API 25. I have also found this. apparently this exists since API 19! I do not wish to start messing and using hacks with the back stack and looking for another solution.

edit 2

here is how i launch a new activity

Intent intent = new Intent(context, ActivityFavoriteShows.class);
intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
context.startActivity(intent);

and here is my manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.somepackage">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
        android:name=".pojos.MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".activities.ActivityMain">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <activity
            android:name=".activities.ActivityShowInfo"
            android:theme="@style/MaterialDrawerTheme.Light.DarkToolbar"/>
        <activity android:name=".activities.ActivitySeasons"/>
        <activity android:name=".activities.ActivityCast"/>
        <activity android:name=".activities.ActivityCrew"/>
        <activity android:name=".activities.ActivitySearch"/>
        <activity android:name=".activities.ActivityFavoriteShows"/>
        <activity
            android:name=".activities.ActivitySettings"
            android:theme="@style/AppTheme"/>

        <service
            android:name=".services.ServiceReadWrite"
            android:exported="false">
        </service>

    </application>

</manifest>