When my theme’s Gutenberg blocks displayed raw HTML and reverted the Block-Library version that fixed the problem – WP Reset

Developing WordPress themes can be an exciting experience, until suddenly something breaks. That’s exactly what happened recently when a routine update caused all my custom Gutenberg blocks to abruptly display 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 went back to normal. Here’s how I unraveled the mystery that turned stylized 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 appear as raw HTML instead of as visual components. In researching the problem I discovered a major change in the block library version I had just updated. Rolling back to an earlier, stable version immediately resolved the display issue. The experience underscored the importance of version locking and thorough testing before updating libraries in WordPress development.

The shocking discovery

I was working on a WordPress theme for a client that used a set of custom Gutenberg blocks. These blocks were behaving beautifully, until one day I refreshed the editor and saw something horrifying. Each block appeared as unparsed HTML code. Instead of rendering rich components like buttons, image galleries, or call-to-action panels, I found myself staring at lines of code like:

  
Join Us Today!

Initially I suspected that I might have accidentally disabled shortcode parsing or caused the block metadata to be desynchronized, so I began the tedious process of debugging. Console logs revealed no error messages and the blocks still appeared in the block inserter. It wasn’t until I went back through my recent dependencies updates that I realized I had just updated 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 bringing in packages directly from the @wordpress NPM namespace, including:

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

This arrangement generally ensures that the block behavior is consistent with the core implementation. However, these packages are actively developed, and that also means breaking through changes. It turned out that I accidentally downloaded a newer version of it @wordpress/block-library that had introduced subtle internal changes to the way custom blocks were registered and parsed.

One of the most important changes was to the way the block parser validated a block type. My blocks were still technically valid, but in the new version some internal functions quietly failed because some metadata was not perfectly aligned. Instead of generating error messages that could be easily caught and debugged, they simply displayed the raw HTML of the block in both the editor and the frontend.

The debugging process

If you’ve ever tried to troubleshoot block rendering problems, you know that debugging Gutenberg is a unique challenge. The way blocks serialize and deserialize content means that even small differences in the storage and editing functions can cause major display problems. Here’s how I solved the problem step by step:

1. Block registration checked – All blocks were still registered and selectable from the inserter.
2. Reviewed the saved content – The content was still correct in the message database and had not changed. That meant the problem wasn’t data loss or migration.
3. Manually tested by re-adding blocks – When I deleted a block and added it again, it displayed correctly… until I refreshed the page.
4. Reverted to a previous commit – When reverting to a previous version of my package-lock.jsonsuddenly everything worked again. That isolated the problem to a dependency update.

After identifying the culprit package, I consulted the GitHub changelog for it @wordpress/block-library and found a recent change regarding serialization and blockContext. Things clicked: my blocks didn’t take those new parameters into account, and the updated library could no longer parse or display them correctly.

Solution: Roll back the block library version

The simplest solution was to reverse the @wordpress/block-library version to a version that previously worked without any problems. Here’s how that was done:

npm install @wordpress/block-library@12.5.0

Followed by a complete rebuild of the assets:

npm run build

And just like that, the modified blocks started rendering normally again. No more raw HTML. No more confusion. The rollback worked like a time machine, returning my theme to the stable behavior it had before the update disaster.

Long-term solutions and prevention

While the rollback made everything work again, it wasn’t a real solution; it was a temporary patch. To ensure future stability, I have taken the following additional steps:

• Pin version – I have locked all critical Gutenberg related packages in my package.json so automatic updates wouldn’t break things again.
• Implemented integration testing – A series of snapshot tests now verify that blocks are displayed as expected in both the editor and on the front end.
• Subscribed to Gutenberg Changelogs – I now regularly review Gutenberg GitHub releases to spot the most important changes in advance.

Lessons learned

This experience provided some valuable insights for anyone working with custom themes in WordPress:

1. Never blindly update production dependencies. Just because there is a newer version does not mean it is backwards compatible.
2. Monitor the Gutenberg GitHub repository for any changes to block behavior.
3. Use local test sandboxes to isolate updates and changes before applying them to real themes or client sites.
4. Always pin your versions unless you use a carefully managed monorepo installation that supports automatic testing of all downstream components.

Closing thoughts

While it was disheartening to see my beautiful custom blocks reduced to lifeless HTML, this experience provided a great crash course in the intricacies of Gutenberg block lifecycles. It also highlighted the importance of monitoring dependencies and understanding how under-the-hood changes can affect your theme’s displayed output.

If you build or maintain WordPress themes using the Gutenberg framework, keep an eye on all your dependencies, track the packages that affect block behavior, and 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 installation command gone wrong.