If you know for sure that you’ve selected a value for every post then I’m lost as to why you’d be seeing these results.
The things that come to mind are
1) Not all values are set
2) There is another field somewhere on this post type that’s using the same name, you could try changing the field name
3) You’re getting a value from a different post or some unknown location, this can happen if you are not inside “The Loop” when getting the value
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