Q: Sleep issue with the new imac

go to

>System Preferences>Energy Saver

check your sleep and display sleep settings or use "restore defaults" if you are unsure of how you want it set up

go to "Schedule..." and make sure you do not have the computer shutting off or sleeping on a weekly or daily schedule unless you want it to.

if the problem persists it could be a conflict with another software installed on your mac, or a conflict with another bluetooth device. If you have a wired USB mouse try connecting that instead of the MM to test, any brand should work.

After 4 hours of Sleep, an iMac (Late 2012) and later goes into Safe Sleep. You need to press the power button once to wake it.

If your Mac doesn't sleep or wake when expected - Apple Support

If you see a progress bar when your Mac wakes from sleep - Apple Support

Do steps 1 thru 4 and fully test the results before moving on to step 5.

1. Reset the SMC, as per > Reset the System Management Controller (SMC) on your Mac - Apple Support

2. Apple > System Preferences > Bluetooth > Advanced > Allow Bluetooth devices to wake this computer

If the box is unchecked, check it.

If checked, uncheck and recheck to reset the plist.

3. Apple System Preferences > Energy Saver > Computer Sleep- Put hard disk to sleep-Enable Power Nap

Set Computer sleep to Never.

Uncheck Put hard disk to sleep when possible.

If Power Nap is unchecked, check it.

If checked, uncheck and recheck to reset the plist.

4. Run the 10.11.4 Combo Update over the top of the current OS X version

Download OS X El Capitan 10.11.4 Combo Update

5. Reinstall the OS X

OS X El Capitan: Erase and reinstall OS X

I find that clicking on the Shift key is much more effective and less prone to accidentally initiating a mouse click action.