Feature flag experience continuity bug (iOS, Android, Flutter, likely React Native)

[ioannisj]

Ticket: https://posthoghelp.zendesk.com/agent/tickets/45321

Users get re-bucketed after identify() despite "Persist flag across authentication" being enabled.

There seems to be a race condition: when preloadFeatureFlags (default: true) is in flight and user calls identify(), the subsequent reloadFeatureFlags() is dropped instead of queued.

iOS - PostHogRemoteConfig.swift:266-271
Android - PostHogRemoteConfig.kt:341-344

Both have:

if loadingFeatureFlags {
   return  // ← Dropped, never sends $anon_distinct_id
}

First request completes without $anon_distinct_id → server never stores hash key override → user re-bucketed.

A potential fix is to queue pending reload instead of dropping:

if loadingFeatureFlags {
   pendingFlagsReload = true  // ← Queue it
  return
}
// After request completes, check pendingFlagsReload and retry

• iOS
• Android
• Flutter (bump min native versions when completed)
• React Native

[marandaneto]

@ioannisj, could you explain the issue and its severity?Ii kinda don't get what the user has to do to run into this bug.
eg a sequence of public apis call, etc? how to repro this?

[ioannisj]

Hey so basically what the description says, we drop /flags calls when there is one in flight already, but we shouldn't cause the user may have identified by then and we should reload with new distinct_id

I think this happens when calling identify() right after SDK init with preloadFeatureFlags=true

Timeline:
──────────────────────────────────────────────────────────────────────────────
SDK init with preloadFeatureFlags=true
    │
    └─→ reloadFeatureFlags() → loadFeatureFlags(distinctId: "anon_123", anonymousId: nil)
                                    │
                                    ├─→ loadingFeatureFlags = true
                                    └─→ API request in flight...
                                                   │
    User calls identify("user_abc")                │
        │                                          │
        ├─→ setAnonymousId("anon_123")             │
        ├─→ setDistinctId("user_abc")              │
        └─→ reloadFeatureFlags()                   │
              │                                    │
              └─→ loadFeatureFlags(...)            │
                    │                              │
                    └─→ if loadingFeatureFlags {   │
                           return  ← DROPPED!      │
                        }                          │
                                                   │
                            API response arrives ──┘
                            (with distinctId: "anon_123", anonymousId: nil)
                            Server has NO $anon_distinct_id → re-bucketing

[ioannisj]

js sdk seems to be doing what's suggested in the description

Not 100% sure if we should queue the net calls or if we can execute them in parallel and just execute their callback logic in order.

[marandaneto]

gotcha, makes sense, if we have a flag that at the end of the current call, if _additionalReloadRequested is true, we have to reload again, and then mark it to false.