players.stats is sometimes returning invalid values for XP, as you can see by the null values in the response shown below:
{"ok":1,"level":20,"xp":null,"xp_max":null,"currants":25326,"energy":281,"energy_max":520,"mood":384,"mood_max":520}
Note that this isn't happening consistently - a response received a couple of seconds earlier contained the correct values:
{"ok":1,"level":20,"xp":4811,"xp_max":12985,"currants":25326,"energy":281,"energy_max":520,"mood":384,"mood_max":520}