If you have paired your MX Master mouse with a Mac running OS X 10.10.2 using Bluetooth Smart, there is a chance your mouse will lose its connection to the computer after it has gone into sleep mode for about two hours.

Try the following: 

1. Turn off the Bluetooth connection, using the Bluetooth icon in the Menu bar.

   

2. Turn the Bluetooth connection back on.

   

Note that there are several factors that might cause connectivity issues, such as Bluetooth interference or you're using a laptop that is connected to an external monitor. You can try un-pairing all of your devices and then re-pair the MX Master mouse. This may resolve the issue. You can also use the Unifying receiver included with your mouse to connect to the computer.

Logitech is aware of this potential connectivity issue and is working on an update.