There are two settings to check. We have attempted to troubleshoot this as a mod team previously and successfully.
First, are the buildings assigned to a dispatch center? If so, check in the settings of the dispatch center. Open the dispatch center hit edit then check the box that says: "Create your own coverage area. Stations belonging to this dispatch center are considered for missions in the assigned dispatch center area."
Secondly, it's important to assign all stations to a dispatch center. If you have two dispatch centers with buildings assigned and build a police station and leave it unassigned then each dispatch center will count the additional PD station in the algorithm.
If you have questions, please let me know as I experience this same problem.