GA4/GTM Multi-Domain Tracking Fix

I’m looking for an experienced Analytics & Tracking specialist (Google Tag Manager + GA4 + Google Ads) to fix a data contamination issue between two domains and two Google Ads accounts.

My situation:

I have two different domains (two websites).

I have two separate Google Ads accounts (each domain should have its own Ads account).

Previously, I used one GTM container for both domains.

I created a new GTM container for one domain, but I still see that the website is loading/seeing multiple containers or tags, causing duplicate tracking and mixed/contaminated analytics data.

The websites run on WordPress, and I’m using a Google Tag Manager plugin. I also use caching/performance optimization (e.g., NitroPack or similar) which may affect tag loading.

What I Need From the Specialist

Diagnose the exact source of the overlap/duplication, such as:

GTM / gtag.js installed more than once (theme + plugin + GTM)

“Destinations / Connected tags” causing data to be sent to another GA4 property

Cache/performance tools delaying, combining, or duplicating scripts

Incorrect triggers/events firing multiple times

Clean up and rebuild the tracking setup so it becomes:

Each domain loads one GTM container only

Each domain uses one GA4 property/stream only (correct and isolated)

Each domain is connected only to its correct Google Ads account (conversions + remarketing)

No unexpected Tag IDs appear in Tag Assistant / Network requests

Implement the fix and document it:

Remove any extra/duplicate tracking code from WordPress theme/plugin settings

Correctly configure GTM tags (Google Tag/GA4/Ads + Conversion Linker, etc.)

Adjust cache settings to exclude GTM/GA scripts from delay/merge if needed

Final validation using Tag Assistant + Chrome DevTools Network

Provide a short report: root cause, changes made, and how to avoid this issue in the future

Deliverables

Each domain running one container only with no duplicate loads

GA4 tracking working correctly (page_view/events) with no duplication

Google Ads conversions working correctly with no cross-account/domain data

List of required cache exclusions (if applicable)

Brief documentation (steps + screenshots or a short recording)

Requirements

Proven experience with GTM + GA4 + Google Ads + WordPress

Experience troubleshooting caching tools like NitroPack is a plus

Work done safely (limited access or screen-sharing if needed)

Quick Notes

Platform: WordPress

GTM plugin is installed

Current issue: multiple containers/tags detected and tracking data mixing between domains

Goal: clean separation—one domain = one GTM container + one GA4 + one Ads account