Cognito Userpools failed to get session

Describe the bug
Friday opened the app and it runned in background thread, when Monday I make the app in front, the error occuces.

Environment(please complete the following information):

• AppSync SDK Version: 3.1.1

Device Information (please complete the following information):

• Device: HuaWei P30
• Android Version: Android 10 (EMUI 11.0.0)

Additional context

2021-02-01 10:16:42.186 13424-29995/? E/AndroidRuntime: FATAL EXCEPTION: Thread-237
    Process: PACKAGENAME, PID: 13424
    java.lang.RuntimeException: Cognito Userpools failed to get session
        at com.amazonaws.mobileconnectors.appsync.sigv4.BasicCognitoUserPoolsAuthProvider.fetchToken(BasicCognitoUserPoolsAuthProvider.java:80)
        at com.amazonaws.mobileconnectors.appsync.sigv4.BasicCognitoUserPoolsAuthProvider.getLatestAuthToken(BasicCognitoUserPoolsAuthProvider.java:86)
        at PACKAGENAME.common.aws.AWSClientFactory$1.getLatestAuthToken(AWSClientFactory.java:37)
        at com.amazonaws.mobileconnectors.appsync.SubscriptionAuthorizer.getAuthorizationDetailsForUserpools(SubscriptionAuthorizer.java:160)
        at com.amazonaws.mobileconnectors.appsync.SubscriptionAuthorizer.getAuthorizationDetails(SubscriptionAuthorizer.java:85)
        at com.amazonaws.mobileconnectors.appsync.WebSocketConnectionManager.requestSubscription(WebSocketConnectionManager.java:92)
        at com.amazonaws.mobileconnectors.appsync.AppSyncWebSocketSubscriptionCall.execute(AppSyncWebSocketSubscriptionCall.java:48)
        at PACKAGENAME.activities.chat.RoomMessageView.prepareOnUpdateRoomLastReadDateByRoomObserver(RoomMessageView.java:1614)
        at PACKAGENAME.activities.chat.RoomMessageView.access$3400(RoomMessageView.java:104)
        at PACKAGENAME.activities.chat.RoomMessageView$24.run(RoomMessageView.java:1465)
        at java.lang.Thread.run(Thread.java:929)

Start with BasicCognitoUserPoolsAuthProvider.fetchToken and getLatestAuthToken, then follow the call path through SubscriptionAuthorizer and WebSocketConnectionManager. Reproduce the failure after the app remains in the background and returns to the foreground on the stated Android environment; done means the reported session-fetch failure is understood and the affected subscription flow is verified.