In Android, we prepare the crash report when the app and SDK are still alive and on "last breath". Therefore we report the user identifier if SetUserIdentifier is called before the crash.
In iOS, when the app is crashing we record the crash details without any additional metadata and let the app exit. When application is started again after the crash, we submit the crash data saved from the crash happened before and additional metadata (such as user ID) known at the time of submission. Please make sure to set user ID before the init.
One way to create consistency is to leave breadcrumb with user ID. The information will be in breadcrumbs field. Breadcrumbs are attached to the corresponding crash report. Number of breadcrumbs is limited to 16 and older breadcrumbs will be dropped.