RemoteConfig.configValue(forKey:) returns default value - firebase

Question

I'm using Firebase Remote Config with Firebase A/B Testing on iOS.
I see a value received from Remote Config sometimes reset to default value.
I think, activated config values does not delete even if server cache on the app has expired.
Is there any situation that activated values are back to the default value?
In-App: Default Value A set.
fetch -> activate
Got B from the server.
Leave apps.
Several hours later, I come back to the app, it seems the value is reset to A.
fetch and activated a strategy
The app activates remote config values once at launch time.
https://firebase.googleblog.com/2017/01/firebase-remote-config-loading.html
Strategy #3: Load values for next time
When your user starts up your app, you immediately call activateFetched(). This will apply any old values you've previously fetched from the cloud. And then your user can immediately start interacting with your app. In the meantime, you kick off an asynchronous fetch() call to fetch new values from the cloud. And in the completion handler for this call… you do nothing. Heck, you don't even need to add a completion handler in the first place. Those values you fetched from the cloud will remain stored locally on the device until your user calls activateFetched the next time they start your app.
ABTesting Settings
target user: 100% of the app
variant-key -> SOME_KEY
Control Group: 50% -> value = A
Variant B: 50% -> value = B
Pods versions from Podfile.lock:
- FirebaseABTesting (2.0.0):
- FirebaseRemoteConfig (3.1.0):
How to set defaults, get values
Default Value is:
RemoteConfig.remoteConfig().setDefaults(["SOME_KEY": "A"])
To get Value from Remote Config:
let value = RemoteConfig.remoteConfig().configValue(forKey: "SOME_KEY")
App Launch Sequences
At first app launch
activateFetched()
got value A(=default).
There is no fetched value yet, activateFetched has no effect.
then fetch.
next time app launch
activateFetched()
got value B (if the user is selected ABTestring's value 'B')
then fetch.
next time app launch
activateFetched()
got value A (this is the issue)
then fetch.
In the above situation, if the app fetched and activated value B,
the value is persisted in activated values cache and
the cached value doesn't reset to A I thought.
Is the assumption right?
Addtional Info
When the app got B from configValue(forKey: "SOME_KEY")
then remoteConfig.allKeys(from: .remote, namespace: NamespaceGoogleMobilePlatform) returns ["SOME_KEY"].
But when the app got A back from 'B' (the last situation in above launch sequence),
then remoteConfig.allKeys(from: .remote, namespace: NamespaceGoogleMobilePlatform) returns empty.