Duplicate events generated due to two significant bugs in GA4 and server-side GTM
In the ever-evolving world of digital marketing, organizations relying on e-commerce implementations have been hit by a significant bug affecting conversion tracking accuracy and revenue attribution. The service worker duplication bug, as it's come to be known, has caused misleading event count estimates in Google Analytics 4's (GA4) dashboard, failing to match actual BigQuery data volumes.
This bug stems from a problem in how Google's gtag service communicates with the service worker component, preventing proper event acknowledgment. Matteo Zambon, a Google Tag Manager and Analytics expert, and Giovani Ortolani Barbosa, a digital analytics specialist, have documented these technical issues affecting GA4 and server-side GTM in recent weeks.
The duplication typically excludes events that fire during page load, as the service worker may not be up yet during initial page rendering. This bug has disrupted the intended functionality of Google tag leveraging service workers to enhance data collection reliability.
To address this issue, Google has introduced enhanced app measurement capabilities as part of its broader tracking infrastructure changes. However, organizations implementing custom event data import functionality face additional complexity from these bugs.
Current workarounds for this bug include blocking specific service worker files or removing iframe elements through JavaScript implementations. Matteo Zambon advises businesses to "always verify your event count directly in BigQuery" rather than trusting GA4's internal estimates.
The bug also affects cost planning for organizations approaching GA4's free tier limits, as the BigQuery estimation issue inflates event numbers for multiple platforms, potentially leading to unnecessary costs.
Google officially announced service worker integration for enhanced GTM server-side data transmission on March 4, 2025. However, the duplication bug surfaced in community reports about duplicate events in server-side GTM implementations as early as September 2024.
Organizations raising issues with data collection when using Google Analytics 4 with server-side Google Tag Manager include privacy advocates and regulatory bodies concerned about user consent requirements and data protection compliance under laws like GDPR. Marketers are also worried about reduced data availability due to low user opt-in rates similar to Apple's App Tracking Transparency. These challenges stem from increased user consent thresholds and limitations on third-party cookie tracking, which affect data quality and usage in marketing and analytics contexts.
Google has unified the Tag Assistant tool as part of ongoing platform modernization efforts. Moreover, the company announced BigQuery schema additions with batch_page_id and event ordering fields in July 2024, aiming to improve data management and analysis.
As the digital marketing landscape continues to evolve, it's crucial for technical teams managing GA4 implementations to immediately audit their current tracking setups to check for duplicate events in server-side containers and compare GA4 dashboard estimates against direct BigQuery queries. By staying vigilant and proactive, organizations can ensure accurate data collection and informed decision-making.
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