Incorrect display, need to reload the page.

I can't tell from this report but I assume these are 404 errors? The browser console will show them, if you would please check there.

If so, this is probably caused by the way CSS and JavaScript assets are concatenated has changed in recent Drupal releases. What is the web server platform configuration?

Hello,
thanks for your quick answer.
I opened Firefox console and browsed the web site with display problems. While I had display problems, no information was filed in the console. No error, no warning, no CSS related item; and no 440 errors.

About web server platform configuration ?
I do not clearly get what type of information would be interesting for further investigation.
I use a standard web hosting service from OVH (in France). Which configuration parameters should be looked at ?

The web server type (Apache? nginx?) and its configuration would be helpful.

Apache.
I have always considered it as a "blackbox service". So I have no idea about its configuration and I never tried to get into it.

Well I see more issues with nginx and Drupal's asset system so we can ignore nginx as a cause. I am astonished there are not 404 errors, and if there really are none, then I don't really know where to look next.

Have you taken the step of comparing (diff-ing) the HTML output of a page with a broken layout vs the same page with a working layout? If not, that is something you could consider doing. It would provide more information.

Are there no errors logged by Drupal?

Hello,
thank you once again for your quick answers.
I am not an html geek. I am not sure to rapidly see the point that leads to this situation of broken layout.

See attachment. HTML output of the same page, one with broken layout, the other with working layout. The output with working layout was the result of reloading the page with incorrect display.

Thansks for your help.

PS : I have sites using Drupal 9, aside the ones with Drupal 11, on the same platform, with parallel repositories below a single /www . I never had this problem with Drupal 9 sites.

Hello,
some more information on what I observe (using Firefox).
Most of the time the page is displayed without delay and lhe layout is OK.
When the page is not immediatly displayed (a 4-5 seconds delay), it finally comes with a broken layout.

You can get access two sites which are hosted under the same /www; those are tests sites :
- a Drupal 9.5.11 site : https://asapidev.fr/echangesd9/; I never observered display problems on this site
- a Drupal 11.1.5 site : https://asapidev.fr/migrationtest/web/; the site on which I observe the display problems

If necessary, I can create an account for you on these sites if it helps.

Screen shots referenced in previous comment.

I go back to your first comment :

"If so, this is probably caused by the way CSS and JavaScript assets are concatenated has changed in recent Drupal releases."

I have desactivated " CSS and JavaScript assets concatenation" in the "development-->performance" configuration.

As far as I have seen while browsing intensively the site, no broken layout appeared.
I will see in the next days if this is confirmed.

If it is the case, it might be wise to have concatenation desactivated by default.

This could be 🐛 Aggregation not working css and js cache directories not being created Active .

Hello,
thank you very much for your support.
It helped me in solving the problem I encountered. After having deactivated the " CSS and JavaScript assets concatenation", and several days of browsing on the site, I observed that the "broken layout" problem has disappeared.

I read the post #3381293. It describes problems linked do "ccs and js aggregation", which might be different from what I obserserved. And some proposed solutions would lead to change things on which I have few knowledge and control.

I still would recommend that " CSS and JavaScript assets concatenation" is not activated by default when installing Drupal. This would prevent people (like me), spending hours and days trying to figure out what was wrong in what was done when installing Drupal, and taking some of your time for helping us.

Also, in the "developement-performance" configuration, a description of potential problems when using this option, or a link to a specific documentation would be appreciated.

There are consequences of not having concatenation enabled, like additional data transfer for your hosting provider and visitors.

Some of the system module form fields have additional documentation if you enable the help module, but not these. It’s an interesting idea to improve that documentation or to enhance the inline field help text in the way you are suggesting. Consider opening an issue for that.