Developing WordPress themes can be an exhilarating experience—until something suddenly breaks. That’s exactly what happened recently when a routine update caused all of my custom Gutenberg blocks to abruptly render as raw HTML both in the editor and on the front end. At first glance, things looked apocalyptic. But after a tactical rollback of the block-library package version, everything returned to normal. Here’s how I unraveled the mystery that turned styled blocks into digital gibberish—and what developers can learn from my unexpected debugging journey.

TL;DR

A recent update to the Gutenberg block-library package caused custom blocks in my WordPress theme to render as raw HTML instead of visual components. Investigating the issue led me to discover a breaking change in the block-library version I had just updated. Rolling back to a previous, stable version immediately resolved the rendering problem. The experience underlined the importance of version pinning and thorough testing before updating libraries in WordPress development.

The Shocking Discovery

I was working on a client WordPress theme that used a series of custom-built Gutenberg blocks. These blocks had been behaving beautifully—until I refreshed the editor one day and saw something horrifying. Every block was appearing as unparsed HTML code. Instead of rendering rich components like buttons, image galleries, or call-to-action panels, I was staring at lines of code like:

<div class="custom-cta">
  <h2>Join Us Today!</h2>
</div>

Initially, I suspected that maybe I had accidentally disabled shortcode parsing or caused the block metadata to desynchronize, so I began the tedious process of debugging. Console logs revealed no error messages, and the blocks still showed up in the block inserter. It wasn’t until I scrolled back through my recent dependencies updates that I realized I had just refreshed the Gutenberg block-library.

Understanding What Went Wrong

WordPress relies heavily on the Gutenberg component libraries to manage block rendering both in the editor and on the front end. My theme was pulling in packages directly from the @wordpress NPM namespace, including:

  • @wordpress/block-library
  • @wordpress/blocks
  • @wordpress/components

This setup typically ensures that block behavior is consistent with the core implementation. However, these packages are developed actively, and that also means breaking changes. It turned out that I had inadvertently installed a newer version of @wordpress/block-library that had introduced subtle internal changes to how custom blocks were registered and parsed.

One of the key changes involved how the block parser validated a block type. My blocks were still technically valid, but in the new version, some internal functions failed silently when certain metadata wasn’t perfectly aligned. Instead of throwing error messages that could be caught and debugged easily, they simply rendered the block’s raw HTML in both the editor and the front end.

The Debugging Process

If you’ve ever attempted to untangle block rendering issues, you know that debugging Gutenberg is a unique challenge. The way blocks serialize and deserialize content means that even minor discrepancies in save and edit functions can create major rendering issues. Here’s how I debugged the problem step-by-step:

  1. Checked the block registration – All blocks were still registered and selectable from the inserter.
  2. Reviewed the saved content – The content was still in the post’s database correctly and hadn’t changed. That meant the issue wasn’t with data loss or migration.
  3. Manually tested re-adding blocks – When I removed and re-added a block, it rendered correctly… until I refreshed the page.
  4. Reverted to a previous commit – Upon rolling back to a previous version of my package-lock.json, suddenly everything worked again. That isolated the issue to a dependency update.

After identifying the culprit package, I consulted the GitHub changelog for @wordpress/block-library and located a recent change involving serialization and blockContext. It clicked—my blocks didn’t account for those new parameters, and the updated library could no longer properly parse or render them.

Fix: Rolling Back the Block Library Version

The most straightforward fix was rolling back the @wordpress/block-library version to one that had previously worked without issue. Here’s how that was done:

npm install @wordpress/block-library@12.5.0

Followed by a full rebuild of the assets:

npm run build

And just like that, the custom blocks began rendering normally again. No more raw HTML. No more confusion. The rollback acted like a time machine, reverting my theme to the stable behavior it had before the update calamity.

Long-Term Fixes and Prevention

Though the rollback got things working again, it wasn’t a true fix—it was a temporary patch. To ensure future stability, I took the following additional steps:

  • Version Pinning – I locked all critical Gutenberg-related packages in my package.json so auto-updates wouldn’t break things again.
  • Implemented Integration Tests – A set of snapshot tests now verifies that blocks render as expected in both the editor and on the front end.
  • Subscribed to Gutenberg Changelogs – I now regularly review Gutenberg GitHub releases to spot breaking changes in advance.

Lessons Learned

This experience offered a few valuable takeaways for anyone working with custom themes in WordPress:

  1. Never update production dependencies blindly. Just because there is a newer version doesn’t mean it’s backward compatible.
  2. Monitor the Gutenberg GitHub repository for any changes to block behaviors.
  3. Use local testing sandboxes to isolate updates and changes before applying them to real themes or client sites.
  4. Always pin your versions unless you’re using a meticulously managed monorepo setup that supports auto-testing of all downstream components.

Closing Thoughts

While it was disheartening to see my beautiful custom blocks reduced to lifeless HTML, this experience offered a great crash course in the intricacies of Gutenberg block lifecycles. It also highlighted just how vital it is to monitor dependencies and understand how under-the-hood changes can affect your theme’s rendered output.

If you’re building or maintaining WordPress themes using the Gutenberg framework, keep an eye on all your dependencies, track the packages that affect block behavior, and always, always test updates in a development environment.

Because sometimes, the difference between a flawless page layout and a wall of raw HTML is one NPM install command gone wrong.