Currently the "alphabetical" sort option on multiple choice fields only applies to when new records are added through an import. This is a confusing. It does not trigger and re-sort options when adding options manually through the Builder, Live App, etc.
If I choose "Alphabetical", click save on the field, I expect it to re-sort my existing choices, but that doesn't happen.
Knack added this "alphabetical" sort option as a way to prevent re-sorting when users want it a specific order. If you have it set to "Alphabetical" it will re-sort the options after every import.
There should be a higher level of customization here - alphabetical always (when records are added from anyplace) or alphabetical only after import (when you might be adding a large batch of new options).