Inconsistent results when executing JPA's EntityManager.createQuery

Question

I am going crazy about an error in my code involving data persistence in Java (JPA). I didn't develop this and I am not at all knowledgeable about this framework, so, sorry in advance about whatever info I fail to present.

The error in question is that a query created with EntityManager.createQuery (a simply select on a table) returns inconsistent results. That is to say, if I change a value via the interface, save the changes, and then reload the browser again and again, sometimes I will see the new value and sometimes I will see the old value. There seems to be no pattern by which this happens, for all I know it is random. And while this happens, if I query the MySQL database, I always see the correct value (the 'new' value).

I don't know what I should even be looking at. The inconsistent values are retrieved from a class annotated as follows:

@ManagedBean
@ViewScoped
public class DivisoreVolumenticoView implements Serializable {

and the kind of object that this EntityManager.createQuery returns is annotated as follows:

@ManagedBean
@Entity
@Table(name = "divisore_volumetrico")
public class DivisoreVolumetricoBean implements Serializable {

where the inconsistent property (although this would happen with any of them) is:

@Column(name = "nazionale")
private Double nazionale;

and there are a bunch of other methods annotated as @Transient, and the getters and setters for the properties do not have any annotations.

The EntityManager on which createQuery is called is retrieved from class below (and when I execute this on my local environment, with every browser refresh sometimes a new object is created and sometimes it isn't):

public class EMHelper {
    private static final EntityManagerFactory emf;
    private static final ThreadLocal<EntityManager> threadLocal;

    static {
        emf = Persistence.createEntityManagerFactory("persistenceUnit");
        threadLocal = new ThreadLocal<EntityManager>();
    }
    
    public static EntityManager getEntityManager() {
        EntityManager em = threadLocal.get();
        if (em == null) {
            em = emf.createEntityManager();
            threadLocal.set(em);
        }
        return em;
    }

If you can at least point me in the right direction, I'd be very grateful. For example: since the value in the database is always the correct one, should I assume that there is no problem with the persistence of the change? or could the problem be there and the inconsistencies while retrieving it be just a symptom?

Thanks in advance.