The article below may be able to help you with this issue.
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I've quoted some helpful highlights for you:
Make sure Bluetooth is turned on
If the "Show Bluetooth status in the menu bar" option is not enabled in the Bluetooth System Preferences, the Bluetooth icon will not display in the menu bar. Enable this option in System Preferences, then check the status of the Bluetooth icon in the upper right menu bar. If the Bluetooth icon does not appear in the menu bar, restart your computer.
Slide the On/Off switch on the bottom of your mouse to turn it on. Note: If the battery compartment cover is not installed properly the On/Off switch may not function correctly or may be difficult to operate. Remove the battery compartment cover and carefully reinstall it.
- When your mouse is on and paired, and the batteries are charged, the indicator light glows steadily.
From the Apple () menu, choose System Preferences, then choose Bluetooth from the View menu. The Bluetooth preferences pane will list the Bluetooth devices paired with the computer, the status of the devices (paired or connected), and whether Bluetooth power is on or not.
- Click the gear icon and choose "Connect" to connect a device that is powered on.
Keyboard or mouse intermittently stops responding
Click the mouse
- Click the mouse once to reconnect it with your Mac. It may take a moment for the mouse to respond.
- Check the battery level of the mouse. Choose System Preferences from the Apple (), then choose Mousefrom the View menu. The battery level indicator is in the lower-left corner. Replace the batteries if they are low.
Check for signal interference
- Wireless networks that operate on 2.4GHz may cause interference.
- Move cordless phone base stations, microwave ovens, and other 2.4GHz electrical devices away from the Mac if you suspect interference.
- Keep wireless devices within 10 meters (33 feet) of the Mac.
- Avoid putting metal objects between the device and the Mac.
Mouse does not track as expected (jittery, jumpy, slow, fast).
The Apple Wireless Mouse can be used on most smooth surfaces, however if tracking issues occur try these options:
- Choose System Preferences from the Apple () menu, then choose Mouse from the View menu. Set the Tracking slider to adjust how fast the pointer moves as you move the mouse.
- Try using a different surface to see if the tracking improves.
- Turn the mouse over and inspect the sensor window. Use compressed air to gently clean the sensor window if dust or debris is present.
- If multiple Bluetooth wireless devices are in use nearby, try turning them off one at a time to see if the issue improves. Bandwidth intensive devices could affect tracking.
I hope this information helps ....
Have a great day!