`observer: true` not working for custom element

[Prinzhorn]

Check that this is really a bug

• [X] I confirm

Reproduction link

https://codesandbox.io/p/sandbox/swiper-navigation-forked-hq74dw?file=%2Findex.html%3A56%2C6

Bug description

When deleting a slide the slider does not updated and leaves extra space at the far right. Compare this to the core-api version https://codesandbox.io/p/sandbox/swiper-navigation-forked-2x6fjm?file=%2Findex.html%3A64%2C48

If this is not supported in the custom element, then there should be a warning or error when using the attribute, right? Or maybe there is and I don't see it because I'm using the bundled js?

Expected Behavior

No response

Actual Behavior

No response

Swiper version

swiper@11

Platform/Target and Browser Versions

Ubuntu 23.10 with both Firefox 127.0.2 and Chromium 126.0.6478.114

Validations

• [X] Follow our Code of Conduct
• [X] Read the docs.
• [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• [X] Make sure this is a Swiper issue and not a framework-specific issue

Would you like to open a PR for this bug?

• [ ] I'm willing to open a PR

[Prinzhorn]

What's weird is that if you open the sandbox it renders correctly. But if you save it once it will show the described behavior.

The video shows the slider working, then I hit ctrl+s and it breaks. Maybe this is an issue with code sandbox? I've never used this service.

Screencast from 2024-07-02 08-52-34.webm