Hi @ozone31912, thanks for your post about the Slider, I am here to help.
It looks like there is a Slider nested inside of a Form Element and since those are both scripted elements with preset behaviors, it could be that you have found some unexpected, unplanned behavior when using the Slider nested inside the form within the Designer.
The Slider element was not originally made with using that nested inside of a form in order to create a multi-page form in mind.
When I did the steps you mentioned on deleting the slider and then undo, the slider also began to change slides for me as well, so I think there might be something that need to be looked at on how the slider nested in the form behaves in the Designer and I can help to check this further.
In the meantime, I would probably recommend to do a publish to the staging domain only, not the custom domain to test that your changes are working as expected.
What you might do is to do the following:
Create a Backup to save the current state of the site: Save & restore backups | Webflow University
Make your changes to the Slider/Form and then publish your site to the webflow.io staging domain (keep the custom domains unchecked with publishing so that the current published custom domain is not affected)
Test on the published staging site url that things work as expected
If things work ok, publish to the custom domain
If things do not work ok, you can keep things as they are or restore to the backup.
Another option is to create a duplicate of the site and test on that, see how to duplicate the project: Duplicate, transfer, or delete a project | Webflow University