Connection impossible after sleep - reboot needed (OS X)

My MBL 2TB has been working more or less without any problems at all for several months, but a few days ago I started having problems.

When the MBL went into sleep, I simply could not wake it up. I couldn’t access it via Finder (normally and via Connect to Server), I couldn’t SSH into it, rebooting the computer didn’t help - I had to pull the plug on the MBL to force a reboot. This happens intermittently, so not always. Also, when the MBP goes to sleep (when I close the lid), often it refuses to accept to reconnect to the MBL, it says it can’t find it. Rebooting the computer doesn’t help - I have to reboot the MBL by pulling the plug.

No FW updates, no OS updates, the only difference is that I used to connect to the router using an ethernet cable, but now I use wifi.

Does anyone know what might be the problem and how to fix it?

Are you able to access the drive from a different computer?

As a recommendation, try resetting the unit with the hard reset button on the back of the unit.

How is the light on the unit?