Mac wakes up after a few seconds: System Wake Reason not found
I did a clean install of MacOS and it completely solved the issue.
Just to be clear, I deleted EVERYTHING off the hard drive and re-installed MacOS. So basically it was a software issue.
I went through everything on Apple’s website to isolate the problem. Finally called Apple support who worked with me for 1-2hrs. Then finally just recommended a clean install. And bam, fixed.