BugWP logo BugWP
Back to Community
Home / Community / Plugin → Gtm4wp – a google tag manager (gtm) plugin for wordpress

Troubleshooting Common GTM4WP Data Layer Issues: Post Terms, Encoding, and Timing

13 threads Sep 16, 2025 Plugin → Gtm4wp – a google tag manager (gtm) plugin for wordpress

Content

Users of the 'GTM4WP – A Google Tag Manager (GTM) plugin for WordPress' often encounter a few specific types of challenges when working with the data layer it generates. Based on community reports, issues frequently fall into three main categories: problems with the Post Terms data, character encoding, and the timing of when the data layer loads. This guide will help you diagnose and resolve these common problems.

1. Issues with Post Terms and Meta Data

A frequently reported concern involves the pagePostTerms data layer variable. Users have found that enabling the "Post Terms" option in the plugin's settings can sometimes lead to unexpected results.

Common Symptoms:

  • Garbled or broken code appearing in the <head> section of your site's HTML.
  • The pagePostTerms object containing a large meta sub-object with data that is not related to taxonomy terms (e.g., rank_math_internal_links_processed).
  • Difficulty in GTM when trying to use an array of terms (e.g., ["6","7","8"]) for a purpose like Google Analytics content groups, which may interpret the array as a single string.

Potential Solutions:

  • Disable the Feature: If the plugin is outputting broken code, the immediate fix is to navigate to the plugin's settings (GTM4WP -> General -> Basic Data) and uncheck the "Post Terms" option. This will stop the plugin from generating the problematic output.
  • Custom Filter for Meta Data: The extraneous meta data appears to be included by the plugin. A more advanced solution would be to use a WordPress filter to modify the pagePostTerms output and remove the meta key before it is sent to the data layer. This requires custom development.
  • Process Arrays in GTM: For the array issue, Google Tag Manager does not natively handle arrays for fields like Content Groups. You will likely need to use a Custom JavaScript variable in GTM to convert the array into a format that your tag can use, such as a comma-separated string.

2. Character Encoding and Formatting Problems

Another category of issues involves data being formatted incorrectly or displayed with strange encoding.

Common Symptoms:

  • Category names or other text appearing as ASCII codes or in an encoded format instead of the expected language (e.g., Arabic or Traditional Chinese).
  • Numeric data, like a Postal Code with a leading zero (e.g., 07002), losing that zero and appearing as a different number (7002).
  • Inconsistent data where some variables (like postAuthor) display correctly while others (like postCategory) do not.

Potential Solutions:

  • Investigate the Source: The plugin uses standard WordPress functions like get_the_category() to pull this data. The problem may originate in how the data is stored in your WordPress database or how your theme or other plugins are interacting with these functions. Check that your site's character set is configured correctly (UTF-8 is standard).
  • Data Layer Variable in GTM: For the postal code issue, the data is likely being processed as a number, stripping the leading zero. You may need to ensure the value is treated as a text string. This might require modifying the variable in GTM to add the leading zero back or addressing it at the plugin level with custom code.
  • Secondary Dimension in Analytics: If you are seeing "(not set)" in reports, use the "secondary dimension" feature in Google Analytics. Add the "Page" dimension to see which specific URLs are generating the unset values. This can help you identify a pattern, such as the issue only occurring on pages triggered by a specific custom event.

3. Data Layer Loading Timing

Tags firing before the data layer is fully populated is a classic timing issue in GTM.

Common Symptoms:

  • Data layer variables (e.g., postCategory, visitorType) returning as "undefined" in tags that use the "All Pages" trigger.
  • This is a recent development on a site where it previously worked correctly.

Potential Solutions:

  • Change the Trigger: The most effective solution is to change your GTM tag triggers from "All Pages" to "DOM Ready" or even "Window Loaded." This ensures the data layer has been fully populated by the plugin before your tags attempt to read the variables.
  • Investigate Conflicts: A change in timing suggests something on the site has changed. A new plugin, theme update, or performance optimization (like more aggressive caching or script deferral) could be causing the data layer script to load later than it did before. Review recent changes to your site.

Conclusion

Many issues with the GTM4WP plugin can be resolved by methodically checking for conflicts, adjusting GTM triggers, and using GTM's built-in tools like the debug console to inspect the data layer. For more complex problems, such as modifying the structure of the data layer itself, custom code using WordPress filters is often required. The gtm4wp_compile_datalayer filter hook can be used to add, remove, or modify data layer variables before they are output.

Related Support Threads Support