Perhaps the issue is that ACF does not ‘DELETE’ and custom field data which is not posted.
If you have saved a custom field value in the past for ‘slider’ and want to delete it, you will need to save an empty value for this field.
For instance, display the ‘slider’ field and delete all content from it and then update the post.
I think I now understand what you previously described with the conditional logic. Because the ‘slider’ field is hidden, it is not posted, therefor, the DB value is not updated / changed.
Either show the field and save an empty value, or edit the DB and remove the value.
Does that help?
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