[BUG][FEATURE FLAGS] Feature flag changes value even if "Flag persistence" enabled

[Garkavenko]

Feature Flag Value Changes Unexpectedly After identify Call

Issue Summary

I am experiencing unexpected behavior with feature flags and experiments in PostHog. Even though my feature flag persists across authentication events, its value changes after calling posthog.identify.

Steps to Reproduce

I have created a simple repository to reproduce the issue: posthog-feature-flags-bug-reproduce.

To run the reproduction:

node index.js

The setup is a basic Express server that serves an HTML page. The logic is as follows:

• Initialize the PostHog instance.
• Subscribe to onFeatureFlags events.
• Render all feature flag values on the screen.
• Provide an "Identify user" button that triggers posthog.identify on click.

Expected Behavior

When opening the site in an incognito window, waiting for the first flag value to render, and then clicking "Identify user," the feature flag should remain consistent across events.

Observed Behavior

Once in approximately 7–10 attempts, the flag value changes between "control" and "test" after calling posthog.identify.

Steps to Catch the Bug

1. Modify the id and email inside the HTML to be unique.
2. Open a new incognito session (not just a new tab).
3. Wait for the first onFeatureFlags event (flag value renders on the screen).
4. Click on the "Identify user" button.
5. Observe if the flag value changes.

Screenshots

Before identify Call:

After identify Call:

PostHog Account View:

Additional Information

This inconsistency affects experiment allocation and may lead to unpredictable user experiences. Any insights into why posthog.identify affects the feature flag value would be helpful. Let me know if more details are needed!
Project ID: 23437