[5.x]: Matrix edits collapsing parent and 400: Bad Request

[jhealey5]

What happened?

Description

Our client has reported that recently inline matrix blocks are behaving odd. They appear to collapse then reappear when making changes within them, causing the page to jump, e.g: https://gyazo.com/619fa8824541c52014f4932eef124130

Or, they can disappear completely and no longer return, e.g; https://gyazo.com/d0451d4e694e9444aae36073edbf5c14

In the former there's nothing in console but in the latter cases they display a 400: Bad Request error with an "Invalid element UUID" in the response, e.g;

We also seem to be having edits to content reverted alongside the above issues, e.g; https://gyazo.com/05e05947669435ab4eb7c9f761502d03

This seems to occur for various matrix blocks across various entry types, it's not just isolated to one. There's been no major changes recently to the site so we're confused why it's recently started happening.

We're not able to reproduce this on our staging or local environments, it's only happening on production. It's worth noting that we're using Blitz + Bunny CDN but both production and staging are using the same setup, so it's quite hard to pin down the problem. Any ideas what this could be or where to look for answers?

Craft CMS version

Craft Pro 5.8.19

PHP version

8.3.21

Operating system and version

Linux 6.1.0-35-amd64

Database type and version

MySQL 28.1

Image driver and version

Imagick 3.7.0 (ImageMagick 7.1.1-41)

Installed plugins and versions

Amazon S3: 2.2.3
Blitz: 5.12.5
Cache Helper: 1.0.11
Craft Flare: 1.3.2
Formie: 3.1.4
Mix: v1.8.1
Redactor: 4.2.0
Relax: 2.1.0
Retcon: 3.2.1
Retour: 5.0.12
SEO: 5.1.19
Servd Assets and Helpers: 4.2.0

[linear]

CMS-1660

[brandonkelly]

My best guess is that this has something to do with field conditions. Is there a condition in the nested entry type’s field layout that could potentially cause the fields/tab to be hidden, which would then become inverted when the fields/tab get removed, which cause them to be brought back?

You might also try enabling safeMode on production to see if this is caused by a plugin. You can do that without a full deployment by temporarily adding a CRAFT_SAFE_MODE=true environment variable.

[jhealey5]

Hey @brandonkelly There's no field conditions, it's happening with pretty much every nested matrix using separate fields so it's not related to a single entry type / field.

I've just tried with Safe Mode on this morning and I'm still having the same problem.

[jhealey5]

I've also just tried setting CRAFT_AUTOSAVE_DRAFTS=false as it seems to be something to do with that triggering, and it's produced an even more odd behaviour, rendering the cms unusable:

Screen.Recording.2025-11-13.at.07.45.55.mov

The page loads properly, then some ajax on craft side loads and proceeds to remove the fields as it completes. Sometimes all the fields, sometimes not. There's no errors in console when this occurs, nor any errors in the network tab.

Just to add, it's only affecting inline matrix fields. Card based work fine.

[brandonkelly]

Can you send a database backup and your Composer files to support@craftcms.com? We can look into this form there.

[jhealey5]

To anyone having the same problem it turns out this was due to request coalescing on our CDN, without it, it's back to normal.