For fields that can hold multiple values, like repeatable fields or fields that allow for multiple selections, multiple tags may be created and applied to the product as a result of the automatic tagging.
Tags for checked checkboxes, where the value resolves to "true", only hold the field's label e.g. "New look", "Backordered" etc.
Tags for reference fields will contain the referenced object's handle
Automatic tagging occurs whenever you change a value using the editor. This also means that if you enable automatic tagging on a custom field, the tags won't be updated unless you save the custom field with a changed value.
To fix tags for existing values, export the objects and import the exported file unchanged. This will synchronize the tags with the existing values. ACF also offers an API endpoint to trigger the automatic tagging process