It's because that is not a “simple” custom field, but repeater reference field (sub field), which is used in row element within the content. This means that this field does not have a single value for a post, but is used with multiple row items referenced to the post. Therefore it is impossible to order by a sub field, which has no direct relation to the actual post type object, but to the repeated row objects related to the actual post object.
Ordering by custom field will only work with fields that actually store values and not references to multiple items – any fields that is not a repeater field.
Unfortunately I don't think this is possible in any ways.Best,
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