While reconstructing an abandoned voice answer on a web app (iOS user, PostHog + server logs), the person's events showed $browser = 'Mobile Safari', $os = 'iOS', which suggests a normal Safari tab whose cookies persist. The raw UA said otherwise:
Mozilla/5.0 (iPhone; CPU iPhone OS 18_7 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/22H352 Instagram 451.0.0.37.60 (iPhone16,1; iOS 18_7_8; ...; IABMV/1; ...) Safari/604.1posthog-js 1.434.15 classifies this as Mobile Safari. $referrer was https://instagram.com/. That matters for diagnosis: Instagram's in-app browser is a WKWebView with its own cookie store, separate from Safari. If the app identifies an anonymous participant by cookie (a claim, a draft, a cart), the person cannot pick up where they left off by opening the same link in Safari; they arrive as a stranger, and server-side the original claim still blocks them. Also, the IAB rarely fires pagehide when dismissed, so $pageleave is usually missing and the trail just stops.
Query that exposes it:
SELECT properties.$referrer, properties.$raw_user_agent FROM events WHERE $session_id = '<id>' AND event = '$pageview'Markers in the UA: Instagram <ver>, IABMV/1, Facebook's FBAN/FBIOS, FBAV. Don't trust $browser for in-app-browser questions.