Tests sometimes fail on previous_session_id unique column

[Ryan Hill]

Describe the bug

Described in customer ticket, but somehow in the tracking the previous_session_id is sometimes not unique at a session and user table level (where we run the tests). We think this is where someone has ported files to a new phone but then continued to use both devices.

Steps to reproduce

N/A

Expected results

Tests pass

Actual results

Tests fail

Are you interested in contributing towards the fix?

Yes, will reduce the test severity to warn so that the models can still pass but alert people if it fails.