iMac Pro Does Not Wake from Sleep

I am running the following:

iMac Pro (2017)

Processor: 3.2 GHz Intel Xeon W

Memory: 64 GB 2666 MHz DDR4

Startup Disk: Macintosh HD

Graphics: Radeon Pro Vega 56 8 GB

When I conclude my work for the day, I set my iMac Pro to "Sleep" under the apple menu. Then, when I return, I will try to wake it up by moving the mouse around or typing on the keyboard, but it will not wake up.

I am forced to hit the power button on the back, and this also sometimes will not wake the machine up, which then requires holding the button down, effectively re-starting the computer (and defeating the purpose of putting on "sleep" mode). I definitely understand that it should be re-started frequently, but I need to be able to use "Sleep" mode, too.

I have NEVER had this problem with any of my other iMacs.

Please help!