Very difficult 'Wake Up' from sleep mode
For the last several weeks my iMac (Retina 5K, 27-inch, Late 2015—Mojave) has been difficult to wake up after it goes into sleep mode. It takes jiggling with the on/off button in the back of the display and pressing on several keys. Sometimes it down't wake up at all and I must restart.
I have run Disk Utility.
Any ideas will be appreciated!
Ed in Brooklyn