With the update to RC16 I can’t change any document icons because the triangle to display the icon submenu is missing in both the main menu bar and the Binder right-click submenu. I haven’t seen this behaviour in any of the previous betas. See screenshot.
[attachment=0]ScrivRC16-icon-submenu-bug.jpg[/attachment]
You might need to re-install RC16. It’s working fine here on my Windows 10 machine.
[attachment=0]ChangeIcon.jpg[/attachment]
Did that already - it’s beta software after all.
Dug a bit further in. The problem is erratic. Some projects show it, others don’t (even when opened simultaneously).
Then a project that did show it, starts to not to - even within its same open session… 
Grrrr… 
Prefer RC15…
For me the “change icon” works for the very first folder/document I want to change after starting scrivener RC16.
After that I can’t change an icon since the display triangle is missing.
After another restart of scrivener I can once again change one icon
Have done a bit more testing. Your description is indeed a better characterisation of this bug’s behaviour. Thank you.
Hopefully it will be fixed in RC17. I use coloured notebook icons to help label WIP items for easier progress tracking. It’s a pain not being able to do this now.
Seems I’m not alone. … 
Please can you try changing a document icon more than once on your Win10 PC.
Does that still work for you (on both the same and different documents)?
This bug is fixed and will be available in the next update. As a workaround use Ctrl+Alt+Right-Mouse-Click to load directly the Change Icon menu.
Thanks. The workaround works OK for me.