Xamarin forms android: Old notifications are replaced by new notifications in foreground mode.

I have implemented push notification on xamarin forms android project using FCM. But when receive a new notification, old notifications are replaced by the new one. This is happening only when the app is in the foreground mode(when app is in open state). No such issues in background state or killed state. Multiple notifications are showing in background state and killed state.

Following is my notification payload, where webContentList is my message data.

{
 "to" : "dmtfiSvBBM0:APA91bFnHkamMSYgxPuiSfdvKnU8hD_mOqrWijnENNgXVSkSgo1ILH3-uKVCU7Ez2PXXOhtDoobIyKBf5UshVfTmvjSqHgXMRTsqguKCSTjIfGnXrVP-_cNFq2sisshZO-BcfkwKTl-I",
 "collapse_key" : "type_a",
 "notification" : {
      "body" : "This is body",
     "title": "Tech Team",
     "priority":"high",
     "content_available":true
 },
 "data" : {
    "webContentList": [
        {
            "webContentDefinitionId": 818084,
            "pageTitle": "CCD Grade 3-4",
            "pageKwd": "CCD Grade 3-4",
            "pageDesc": "CCD Grade 3-4",
            "siteId": 45,
            "pageCreatedTime": 1555145959428,
            "pageUpdatedDate": 1555927274279,
            "modifier": {
                "userId": 12944,
                "applicationId": 32,
                "username": "robert.downey",
                "email": "robert@master-mail.net",
                "firstName": "Robert",
                "lastName": "Downey"
            },
            "creator": {
                "userId": 12944,
                "applicationId": 32,
                "username": "robert.downey",
                "email": "robert@master-mail.net",
                "firstName": "Robert",
                "lastName": "Downey"
            }
        }
        ]
 },
  "ttl": 3600
}

I removed the collapse_key from the payload, but notifications are replacing in foreground mode.

Please suggest a solution for this issue?