When using Google Analytics with Tag Manager and multiple subdomains, here are the key things to check:

Cross-Domain Tracking: Ensure cross-domain tracking is set up in Tag Manager by adding your subdomains to the linker.autoLink field for proper session tracking across subdomains.

Filter Application: Ensure filters are applied to the correct view in Google Analytics and that they include all necessary subdomains.

Hostname Filters: Verify that your filters for hostnames include all subdomains. Use regex if needed, e.g., ^.*.example.com$.

Triggers: Ensure the Google Analytics tag fires on all pages of your subdomains by using an "All Pages" trigger.

Real-Time Testing: Use Real-Time reports in GA to confirm that your tags and filters are working correctly across subdomains.

Test Filters: Always test filters in a separate view before applying them to the main reporting view to avoid data loss.

Consistent Tracking ID: Make sure all subdomains are using the same GA tracking ID or have the proper setup if using different ones.

This ensures accurate tracking and filter application across all subdomains.

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