For anyone who has the same issue in the future, I think I may have found the culprit on my end. For a couple of weeks, I just resorted to using Hibernate instead of Sleep and didn't think too much of it. However, a couple of days ago, I had to completely uninstall iCUE and Armoury Crate and reinstall them both to regain control over my motherboard's RGB lights through an iCUE plugin. This is the largest change I've made to my system since my last post. Today, out of nowhere, I wanted to try the Sleep feature again, which is now working correctly 5 out of the 5 times I've tested it so far. Should the issue resurface, I will update this post to indicate that it wasn't fully resolved. For the time being, I'm having no issues with my current Windows install; no format or anything else was needed. Cheers!