Mixpanel Events Not Linking to User: Understanding the Issue

I’ve implemented server-side logging for my project using the simplified API. When a user loads my homepage, three events are logged like this:

{
  "event": "APP_LOAD_SUCCEEDED",
  "properties": {
    "distinct_id": "$device:5ff9dcfd-880e-4303-8a7a-131e6aebb724",
    "$device_id": "5ff9dcfd-880e-4303-8a7a-131e6aebb724",
  }
}


{
  "event": "LANDING_PAGE_MOUNTED",
  "properties": {
    "distinct_id": "$device:5ff9dcfd-880e-4303-8a7a-131e6aebb724",
    "$device_id": "5ff9dcfd-880e-4303-8a7a-131e6aebb724",
  }
}


{
  "event": "CREATE_DATASET_SCREEN_MOUNTED",
  "properties": {
    "distinct_id": "iSYUjPGqIrf6wp5oyzbBNLSMx303",
    "$device_id": "5ff9dcfd-880e-4303-8a7a-131e6aebb724",
    "$user_id": "iSYUjPGqIrf6wp5oyzbBNLSMx303",
  }
}

The problem - Mixpanel doesn’t retroactively associate the first two events with the same user once the $user_id is available (see below) Is there a reason Mixpanel isn’t automatically linking these events to the user once the $user_id is identified? Does server-side logging require an explicit call to mixpanel.identify() to achieve this? I do not want to resort to calling identify() from the client because this will be blocked in ~30% of cases.

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