Description

We have multiple iOS apps in production which are using Firebase Analytics and our own internal analytics system in parallel to log their sessions. Our internal analytics system is setup to log all app foreground launches & moves from background to the foreground. When comparing those numbers to the session counts produced by Firebase Analytics we noticed suspiciously high session counts on Firebase Analytics side and decided to investigate further.

When the app is launched in iOS simulator and the -FIRDebugEnabled launch argument is included, the session_start event is emitted by Firebase SDK when the simulator receives a push notification payload with content-available: 1 flag, causing the OS to launch the app to the background. This only happens when more than 30 minutes has passed since the last session start event.

Based on Firebase documentation this should not be happening:

a session initiates when a user either opens your app in the foreground or views a page or screen and no session is currently active (e.g. their previous session has timed out).

In the end, we were able to reduce our GA4 session counts considerably by removing the content-available: 1 field from our push payloads.

A potentially related issue which has been already closed: #6161

Reproducing the issue

• Have an iOS app with push notifications & Remote notifications background mode enabled
• Add -FIRDebugEnabled launch argument in Xcode scheme editor
• Select Launch: Wait for the executable to be launched in Xcode scheme editor
• Select Product -> Run
• Send a push notification to that app in simulator
• Note that the app is launched into background by the iOS
• Note that session_start event is triggered (even though the app is in background), if more than 30 minutes has passed since the last push

Firebase SDK Version

10.18.0

Xcode Version

15.1

Installation Method

Swift Package Manager

Firebase Product(s)

Analytics

Targeted Platforms

iOS