Suspect ist a combination of "failure to thrive" with a subpar feed, aggravated by calcium blocking uptake further. Though that's not necessarily the cause of the constipation, its certainly a source of struggle
If they follow conventional ways of writing that, since a feed is more than fat, fiber, and protein, that's a 5% fiber mix, which is within acceptable ranges. (I'm assuming a 100g serving).
The whole mix is borderline, below targets for an adult layer, as those numbers are generally accepted...