Layers Window Twirl Down Icon Issue
I only know of this occurring on the latest version of Adobe Illustrator CC 2017 for Windows 8.1. In the Layers Windows, there's a very slight graphical bug. A locked group within another locked group is expanded to show what it contains by pressing the sideways "V" shaped arrow to the group's left side. As expected, the arrow plays its animation of rotating into the downward "V" shape and expanding the group. However, when the locked group is compressed down again, the button to expand the group disappears and is unclickable until clicking off to another item in the Layers Window and then clicking back to the original group I was working with. This also appears to only be an issue in Windows. I first noticed this on September 29, 2017, and it's still occurring as of October 14, 2017.
Please accept my sincere apology for the inconvenience. Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.