Conditional fields and blocks not updating properly in production when using Live Preview

[beease]

Describe the Bug

In production environment, when editing a large page with many blocks and Live Preview enabled, the admin UI gets stuck and does not update properly after adding or editing blocks.

More specifically:

• The screen often shows an infinite loading spinner after adding a new block :

• Conditional fields (e.g., checkboxes showing/hiding fields) stop working — toggling them has no visible effect until a manual page reload.

In both case, refreshing the page makes the admin UI appear correctly.

Video:
In this video, I start with a light page, then duplicate some large content — which triggers both bugs:

Enregistrement.de.l.ecran.2025-06-05.a.12.00.30.mov

Additional context:

After extensive testing, the issue only appears when all 3 conditions are met:

• Production environment
• Live Preview enabled
• Document size is large (~30KB or more)

When the request body is small (~10KB), everything works fine. The bigger the document, the more consistent the bug becomes.

Link to the code that reproduces this issue

No repo yet – bug is only reproducible in production (see comment below).

Reproduction Steps

• Create a collection with layout blocks (rich text, nested fields, etc.).
• Enable Live Preview.
• Deploy in production (in my case: self hosted Docker + Nginx setup).
• Edit a large document (with 30KB+ payload).
• Add a new block or toggle a conditional checkbox.

Which area(s) are affected? (Select all that apply)

area: ui

Environment Info

Binaries:
  Node: 22.16.0
  npm: 10.9.2
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  payload: 3.40.0
  next: 15.3.3
  @payloadcms/db-mongodb: 3.40.0
  @payloadcms/db-postgres: 3.40.0
  @payloadcms/graphql: 3.40.0
  @payloadcms/live-preview: 3.40.0
  @payloadcms/live-preview-react: 3.40.0
  @payloadcms/next/utilities: 3.40.0
  @payloadcms/plugin-seo: 3.40.0
  @payloadcms/richtext-lexical: 3.40.0
  @payloadcms/translations: 3.40.0
  @payloadcms/ui/shared: 3.40.0
  react: 19.1.0
  react-dom: 19.1.0
Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Debian 6.1.129-1 (2025-03-06)
  Available memory (MB): 7953
  Available CPU cores: 2

[github-actions]

Please add a reproduction in order for us to be able to investigate.

Depending on the quality of reproduction steps, this issue may be closed if no reproduction is provided.

Why was this issue marked with the invalid-reproduction label?

To be able to investigate, we need access to a reproduction to identify what triggered the issue. We prefer a link to a public GitHub repository created with create-payload-app@latest -t blank or a forked/branched version of this repository with tests added (more info in the reproduction-guide).

To make sure the issue is resolved as quickly as possible, please make sure that the reproduction is as minimal as possible. This means that you should remove unnecessary code, files, and dependencies that do not contribute to the issue. Ensure your reproduction does not depend on secrets, 3rd party registries, private dependencies, or any other data that cannot be made public. Avoid a reproduction including a whole monorepo (unless relevant to the issue). The easier it is to reproduce the issue, the quicker we can help.

Please test your reproduction against the latest version of Payload to make sure your issue has not already been fixed.

I added a link, why was it still marked?

Ensure the link is pointing to a codebase that is accessible (e.g. not a private repository). "example.com", "n/a", "will add later", etc. are not acceptable links -- we need to see a public codebase. See the above section for accepted links.

Useful Resources

• Reproduction Guide
• Contributing to Payload

[github-actions]

This issue has been automatically locked.
Please open a new issue if this issue persists with any additional detail.