We have created a custom dimension in Google Analytics, which is has a unique value for each user. When filtering in the user explorer for the custom dimension matching the exact value any given user, multiple rows appear in the Google Analytics user explorer (one row with our custom dimension displaying as the app instance ID, and another row with 19 numbers as the ID), as though they are separate instances.
The values in each row don't quite match up, but do in some regards: the approximate location, devices/platforms, and even some of the events themselves are identical. They also differ slightly: different user engagement durations, different event counts, and so on. Viewing any event details for either row of data in the user explorer shows that the custom dimension is correctly captured as being identical for both rows.
Is there any reason why this might be happening?
For context: this custom dimension is used to track users from our app, and tie their app use to survey data in a research study. Users go to the web app initially, where they are assigned the value, participate in the research study, and then back to the web app.
We thought that maybe users were being captured on the first instance of the web app (i.e., before participating in the research study) as a separate instance from the second instance of accessing the web app, but the first recorded events have the same timestamp, which wouldn't be possible if that were the case.
We also thought it may somehow be different users, but again, this wouldn't be possible (or highly unlikely) as the first recorded events share the exact same timestamp, and are from the same approximate area, and use the same types of devices.