I have had my EX4 for just over a year. Since day 1 all 4 drive never (never!) stop working. When you have the LEDs in they flash all day and night and you can hear the drives reading/writing. I have verified that devices are not communicating and have even shut down all connected devices and the network for over 2hrs as a test.
I also have it set to sleep when possible but it never does.
I have shut down and restarted many times over the last year.
When I bought the device I worked for several hours with customer service over 3 days and they did not have any idea. We were also working on some connection issues.
I then forgot about it till today.