GutenSlider blocks fail in multisite: missing attribute declarations

Hello,

I am contacting you regarding your extension GutenSlider, which I find very well designed and genuinely useful. It provides features that are valuable for editors, and I would be glad to use it in production environments.

However, I have encountered a significant issue when the extension is used in a WordPress multisite installation. The blocks work correctly in a single-site setup but become unstable or impossible to save in multisite. The symptoms include:

• blocks flagged as “invalid content / attempt to recover”,
• some attributes disappearing after saving,
• page updates failing (“The update failed”),
• different behavior between Super Admin and regular site admins.

After a detailed review, the root cause seems clear:1. The blocks rely on many complex nested attributes…

GutenSlider uses a large set of attributes:

• Desktop / Tablet / Mobile structures,
• JSON-based style and layout objects,
• autoplay, navigation, pagination settings,
• dynamic CSS-related objects,
• various slider configuration parameters.

This level of complexity is normal for a block offering advanced layout control.2. …but these attributes are not declared in the block’s block.json

In multisite environments, WordPress applies strict validation rules:

• REST API schema validation is enforced,
• KSES sanitization is strict for non-super-admin roles,
• attributes not declared in block.json are rejected or stripped.

Since the attributes used by GutenSlider are not listed in the block schema, WordPress:

• removes or alters nested JSON objects,
• invalidates the block when reloading the editor,
• may completely prevent saving via the REST API,
• causes repeated recovery attempts.

This issue does not appear in a single-site installation but is systematic on multisite networks.3. To ensure multisite compatibility, one key step is required

👉 All attributes used by the GutenSlider blocks need to be declared in block.json.

Each attribute should define:

• its type,
• its default value,
• and, when applicable, a full object structure (e.g., Desktop/Tablet/Mobile).

This is necessary for Gutenberg and WordPress multisite to accept the block’s content.4. Suggested approaches for a long-term fix

• Add a complete list of attributes to the block.json files matching the React component usage.
• Test GutenSlider in a clean multisite environment without unfiltered_html.
• Compare with block libraries that handle complex schemas successfully (Kadence, Spectra, GenerateBlocks, etc.).
• If needed, consider using a dynamic block with a render_callback to bypass strict HTML validation.

If you need sample block output or additional technical details to reproduce the issue, I am happy to help.

Best regards,

Laurent