Q: 31% of our traffic landed in 'Unassigned' — what was wrong and how was it fixed?

Q: 31% of our traffic landed in 'Unassigned' — what was wrong and how was it fixed?

A: A campaign-heavy account had a third of sessions in the Unassigned channel. Their UTMs used utm_medium=newsletter, which matches no default channel rule:
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Reports → Acquisition → Traffic acquisition: grouped by source/medium to find the offenders
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Found 'email/newsletter' and 'fb/social-paid' not matching default definitions
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Admin → Data display → Channel groups: created a custom group with rules for those mediums

After the custom channel group applied (it reprocesses historically), Unassigned fell from 31% to 4%, and Email and Paid Social channels finally showed their true volume.

TL;DR: Non-standard utm_medium values dump traffic into Unassigned. A custom channel group reclassifies it — even retroactively.

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