Multiple app instances appear as the same session in Datadog RUM

[3Dayg]

Describe the bug

I am using the library @datadog/browser-rum version 6.22.0, and I noticed that when I open multiple instances of my React app (e.g., in two different tabs or two different instances of chrome), the data collected in Datadog appears as part of the same session, when in fact they are 2 different ones, this causes huge headaches and noise when trying to follow a user journey for debugging.

Based on the documentation's definition of a session, this behavior seems incorrect or ambiguous. The documentation defines a session as "unique user journey":

All RUM data refers to user or synthetics sessions, which are at the top of the event hierarchy. A session is a unique user journey and encompasses everything (for example, pages viewed, views, clicks, scrolls, and errors) the user triggered. A session can last up to four hours of continuous activity, or it can expire after 15 minutes of inactivity. Since a session encompasses the entire journey, all attributes tied to that user are also tied to that session. For example, you may want to query on a default attribute, like action count, then add something more custom, like user attributes.

https://docs.datadoghq.com/real_user_monitoring/guide/understanding-the-rum-event-hierarchy/

To Reproduce
Steps to reproduce the behavior:

1. Open a React app that uses @datadog/browser-rum version 6.22.0.
2. Open the app in two different tabs or two different browsers.
3. Perform actions in both instances of the app.
4. Observe that the data collected in Datadog appears as part of the same session. If i get this right it can also be
   checked running this on console:
   DD_RUM.getInternalContext().session_id

Expected behavior
I expected each instance of the app (e.g., in different tabs or browsers) to generate separate sessions in Datadog, as they represent distinct user journeys. Alternatively, if this behavior is intentional, the documentation should provide clearer guidance on how session IDs are determined and why this behavior occurs.

[mormubis]

Hey @3Dayg,

Thank you for reaching out. First, I would like to clarify the difference between the two tabs or browsers. Could you provide a link where I can test this behavior? Thank you!

Lastly, this is the expected behavior for two different tabs. Most applications allow multiple tabs or pages to open within the same session. I apologize for any confusion. I will inform the documentation team to see if they can improve the writing.

In the meantime, I will remove the bug label until we can reproduce the issue with multiple browsers.