GA4 Channel Groups: Why Sessions Disappear Into (Other) and How to Fix It (2026)

Why does GA4 traffic fall into (Other) or Unassigned?

GA4 assigns sessions to channel groups based on a rule hierarchy matching UTM parameters against predefined patterns. `(Other)` means the UTM values provided don't match any default channel group definition. `Unassigned` means no source/medium information was present at all (direct traffic with no identifiable referrer and no UTM).

The most common cause of (Other) inflation: inconsistent UTM naming on paid social campaigns. Meta campaigns tagged with utm_medium=paid_social fall into (Other) because GA4's default Paid Social channel requires utm_medium to match paidsocial (without underscore) or a set of other patterns. A single underscore causes misclassification.

How GA4 default channel group assignment works

GA4 evaluates session source/medium against its channel group rule set in order. The first rule that matches wins.

The key UTM→channel group mappings

The Paid Social medium values that work

GA4's Paid Social channel group matches utm_medium against this pattern (approximately): paid social | paidsocial | cpv | cpm | cpc | display | banner

Common broken tagging for paid social:

• paid_social ❌ (underscore breaks it)
• Paid Social ❌ (capital letters break it in some implementations)
• social_paid ❌ (wrong order)

Correct tagging:

• utm_medium=paidsocial ✅
• utm_medium=paid social ✅ (URL-encoded space works)
• utm_medium=cpc ✅ (works but conflates with Paid Search — not recommended)

Recommended for Meta, LinkedIn, TikTok:

Platform-by-platform UTM conventions

Meta (Facebook/Instagram)

Use Meta's dynamic UTM parameters (wrapped in {{}}) in the campaign's URL parameters field — they are resolved at the ad level when the ad serves.

LinkedIn

TikTok

TikTok uses __PARAM__ format for dynamic values (two underscores each side).

Microsoft Ads (Bing)

Or use auto-tagging (msclkid) with the Microsoft Ads conversion import. Auto-tagging sets bing / cpc automatically.

Pinterest

Creating custom channel groups in GA4

When default channel groups don't fit your business (e.g., you want a separate "Affiliate" channel or a custom "Partner Email" group), create custom channel groups:

Admin → Channel Groups → + New Channel Group

Example: custom Affiliate channel group

Rule:

• utm_medium exactly matches affiliate
• OR utm_source contains affiliatenetwork

Example: custom CRM Email channel

Rule:

• utm_medium exactly matches email
• AND utm_source contains hubspot OR mailchimp OR klaviyo

This distinguishes CRM-triggered email from cold outreach or other email types.

Important: Custom channel groups only affect the reporting view — they don't retroactively change data. Changes apply from the date the custom group is created onwards.

Diagnosing (Other) traffic in your property

Step 1: GA4 → Reports → Acquisition → Traffic Acquisition → set dimension to Session default channel group

Step 2: Note the (Other) percentage. Over 5% warrants investigation.

Step 3: Change dimension to Session source / medium and filter to rows where Session default channel group = (Other)

Step 4: Examine the source/medium combinations in (Other). The most common patterns:

• facebook / paid_social (underscore) → fix to paidsocial
• newsletter / email_campaign → fix to utm_medium=email
• partner / partner_referral → add to custom channel group

Step 5: Fix UTM tagging at the source (campaign manager or link builder), and/or add a custom channel group rule to catch the existing traffic pattern.