A deep link journey is a chain, not a single event. An ad network, browser, redirect provider, app store and mobile app may all handle the user before an analytics platform receives an event. Attribution fails when one hand-off drops, rewrites or delays the information needed to connect those steps.
Start with observable behaviour. Record the original link, each redirect, the final destination, installation state and events emitted after open. Test on real devices because browser privacy controls and operating-system routing differ from desktop previews.
The most frequent problems are inconsistent campaign parameters, redirect rules that vary by platform, deferred links that expire before first open and conversion events that do not retain the acquisition identifier. A compact test matrix makes these failures reproducible.
Treat unattributed traffic as a measurement signal, not automatically as organic demand. Monitor the rate by operating system, app version and channel after each release. A sudden change often points to implementation drift rather than customer behaviour.