onFeatureFlags isnt triggered on some mobile web devices

[sirpy]

Bug description

We are using posthog-react-native package also on web.
We have encountered an edge case where on some mobile devices with chrome browser the feature flags do not seem to be loaded.

1. posthog.onFeatureFlags callback isnt called
2. using useFeatureFlag* hooks return undefined

Observations:

• When calling posthog.reloadFeatureFlags() it then works
• In network tab we can see that all feature flags are prefetched correctly before calling posthog.reloadFeatureFlags

How to reproduce

1. android chrome 137.0.7151.72
2. call posthog.onFeatureFlags -> nothing happens
3. call posthog.reloadFeatureFlags -> callback triggered

Related sub-libraries

• All of them
• posthog-web
• posthog-node
• posthog-ai
• posthog-react-native

Additional context

Thank you for your bug report – we love squashing them!

[marandaneto]

cc @PostHog/team-feature-flags for initial investigation

[marandaneto]

@sirpy please share your PostHog SDK version and the code snippets of your SDK init setup and also the hooks, the more the better, thanks

[sirpy]

@marandaneto

   <PostHogProvider
            apiKey={import.meta.env.REACT_APP_POSTHOG_KEY}
            options={{
                host: import.meta.env.REACT_APP_POSTHOG_PROXY ?? 'https://app.posthog.com',
            }}
            autocapture={false}
        >

const RoutesWrapper = () => {
    const posthog = usePostHog()
    const [posthogInitialized, setPosthogInitialized] = useState(false)

    useEffect(() => {
        if (posthog) {
            posthog.onFeatureFlags(() => setPosthogInitialized(true))
        }
    }, [posthog])

    return posthogInitialized ? <Routes /> : <Spinner variant="page-loader" size="lg" />
}

posthog-react-native@npm:2.11.5

[marandaneto]

@sirpy please upgrade to the latest version https://github.com/PostHog/posthog-js-lite/blob/main/posthog-react-native/CHANGELOG.md#410---2025-06-12 yours is quite old, can you test again after the changes?

Also, I'd need to know the surrounding code around PostHogProvider and RoutesWrapper so I have a better overview of your setup.