1. Known Diamond problem. Its skin problem.
2. Another skin related problem. Not Windowblinds problem.
3. Cortana is known, not to be skin by Windowblinds because it is using UWP : (Universal Windows Platform) Note : all UWP type apps are normally not skinned.
4. That something that might varies in effect depending on Theme applied. On Diamond the are some problem. Please try other themes. Be reminded, most skin designer has designed their skin to the be best looking to their own perspective. If you change/modify it, the result might varies. Some make it look better, but most of the time it will look worst.
5. UWP apps on both.
6. I don't have realtek Audio on my system. But I think the glitch is on Realtek.
7. If you are talking about those groupy tabs. That is not on Windowblinds. Groupy has it own setting. Its remember the state of windows before its get grouped. If you group a maximized windows with a not maximized windows, sometimes you will see that behavior.
8. That is another Windows 10 strange UI setting that Windowblinds can not change.
9. That on MPC design.
10.That is on Groupy, not Windowblinds. You can always set groupy to be on top of the titlebar instead of in the titlebar. Anyway, as a note, strangely, I can't reproduce your problem on my system even with the tabs in the titlebar. (20++ groupy tabs.)

Side Note : Seem to me that you are very new with Windowblinds. Please note that:
I) Windowblinds will never be able to skin all program perfectly. There are a lot of programs that were designed differently between one another which are totally beyond Stardock/Windowblinds control. For example, As you will see, most web browsers are not skin-able by Windowblinds most probably because they have their own skin/theme system. And MS office suite is another example.
II) Windowblinds will always in development stage and since Windows 10 keep spitting out updates which modified its UI systems almost every month. Which mean that Windowblinds user need to understand if some part it will work now but might not work after Windows 10 updates. I am sure Stardock's Dev team is working very hard to keep up with Microsoft "development". But playing catch up with a bigger team will always be hard.
Please note that this is my personal view. Not official Stardock views.
Thank you,
Basj,
Stardock Community Assistant