Top two reasons I can think of are: 1) Fulfillment policy misconfiguration. 2) Mistake in the software (a.k.a bug).
My recommendation for discerning between the two options: Try requesting the problematic item via the Alma UI – a. If it can be requested in the UI, it’s probably a bug; open a case. b. If it can’t be requested in the UI either, verify the fulfillment policy configuration is as expected. If the configuration is as expected, it may be a bug; open a case.