Could you please confirm if there are any recent changes done to the network?
Is only one AP (R510 model) affected or are more APs affected?
Do you have any other model APs available in the network which works fine?
While the AP drops out the connection, are there any events recorded? Have you tried connecting the Laptop to the APs port to see if the Laptop behaves the same way that the AP behaves? May be you could initiate a continuous ping from the Laptop to the Controller IP by connecting the Laptop to the same port where the affected AP is connected.