I had this issue as well. After doing some research I used the "powercfg" command to troubleshoot it successfully.
You'll need to run the command prompt as administrator and type "powercfg -requests" to see what processes might be active. In my case, under "DISPLAY" my web browser chrome.exe showed up as the culprit.
To override that executable from keeping the system awake, I entered the command "powercfg -requestsoverride PROCESS chrome.exe DISPLAY" (replace chrome.exe with whatever the application happens to be in your case). To check that the override rule was entered
successfully you can type "powercfg -requestsoverride" and in my case chrome.exe showed up under the "[process]" section.
I also had a related problem where my computer would wake back up right after I manually set it to sleep. Using "powercfg -devicequery wake_armed" I saw that my network adapter was one of the devices that could wake my computer (in addition to my mouse and
keyboard) so I disabled that in the Power Management tab under device name in Device Manager.
Hope this helps others,
Tai