Error when editing Read More block CSS in FSE

[marbaque]

Description

Custom CSS section in the FS editor is not working properly. When I edit the Read More block, and click on the CSS Text Area, as soon as I start typing the site crashes.

Here's the error I copied, though it is running in my local machine:
al@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:82327
Pt@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:48526
n/zt/<@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:48385
n@http://oeglobal24.test/wp-includes/js/dist/compose.min.js?ver=84bcf832a5c99203f3db:9:13248
set@http://oeglobal24.test/wp-includes/js/dist/compose.min.js?ver=84bcf832a5c99203f3db:9:13295
updateFill@http://oeglobal24.test/wp-includes/js/dist/components.min.js?ver=865f2ec3b5f5195705e0:26:217394
Yy/<@http://oeglobal24.test/wp-includes/js/dist/components.min.js?ver=865f2ec3b5f5195705e0:26:213479
Ur@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:73201
Jr@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:80402
Zr@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:80258
Gr@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:79798
n/xl/<@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:91178
xl@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:91680
fl@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:85511
Nn@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:32442
pl@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:85802
V@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:9905
Je@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:24935
pe@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:15763
fe@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:15545
EventListener.handleEventZe@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:24448
Xe@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:23909
n/Ge/<@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:24015
Ge@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:23959
n/e.createRoot@http://oeglobal24.test/wp-includes/js/dist/vendor/react-dom.min.js?ver=18.3.1.1:10:127044
QE@http://oeglobal24.test/wp-includes/js/dist/edit-site.min.js?ver=4cfd4c6e8c033bb1b61a:11:638896
@http://oeglobal24.test/wp-admin/site-editor.php?canvas=edit&p=%2Fwp_template%2Foeg-main%2F%2Ffront-page:1800:16
EventListener.handleEventd@http://oeglobal24.test/wp-admin/load-scripts.php?c=1&load%5Bchunk_0%5D=jquery-core,jquery-migrate,utils,wp-dom-ready,wp-hooks&ver=6.8.3:10:307
@http://oeglobal24.test/wp-admin/site-editor.php?canvas=edit&p=%2Fwp_template%2Foeg-main%2F%2Ffront-page:1799:4

Step-by-step reproduction instructions

1. Go to Edit Site
2. Click on the Styles button on the top bar
3. Click on Blocks
4. Click on Read More block
5. Start typing in Advanced > Additional CSS

Screenshots, screen recording, code snippet

Grabacion.de.pantalla.2025-10-09.a.la.s.3.02.35.p.m.mov

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[sidharthpandita1]

works fine for me

https://drive.google.com/file/d/1hVTfEtuhcMDjOlyxTWE1UEyUQkJbyI2o/view?usp=drive_link

[t-hamano]

@marbaque, can you check the following points?

• Does this issue only occur with the Read More block?
• What version of WordPress and Gutenberg plugin are you using?
• Does this happen if you disable all third-party plugins?

[github-actions]

Help us move this issue forward. This issue is being marked stale since it has no activity after 15 days of requesting more information. Please add info requested so we can help move the issue forward. Note: The triage policy is to close stale issues that need more info and no response after 2 weeks.

[t-hamano]

Since there has been no activity for two weeks, I will close this issue. If someone finds an environment or steps to reproduce this problem, please leave a comment.