Three comments on the constantly waking from sleep problem with the iMac Pro. (1) I have an iMac Pro 10-core, 128 GB RAM, 2TB SSD, Radeon Vega64 Pro (16 GB) that began repeatedly waking up after the 10.13.4 update. (2) After hours of trying to resolve this issue, I checked Console>Mac analytics to see what was going on that was initiating these wakeup sleep cycles and found that it was my ethernet network even though I did not have Wake for Network Access checked in Energy Preferences. I Googled the exact wake error found in console and dsicovered
that many others were reporting this issue and the only solution was to disconnect the wired ethernet and use a wireless connection. When one does this the constant wakes from sleep cease immediately and sleep works perfectly on my iMac Pro. (3) the latest OS update (10.13.5) does NOT solve this problem.
This problem has been submitted as a bug report to Apple by others at least two months ago (and by me) and Apple has done nothing to resolve the issue which leaves the 10 GB ethernet port on the iMac Pro useless if you ever want to put the computer to sleep.
I urge those of you who have not done so to submit a bug report to Apple and hopefully one day Apple will decide that the iMac Pro is worth supporting and fix this issue which they themselves created in the 10.13.4 update.
Tom