Looks similar to the report of Rudolf Galan here:

https://rammichael.com/7-taskbar-tweaker-for-windows-10-october-2018-update#comment-10176

Please take a look at our conversation in the comments and see if the tips there help solve your problem.

See:
https://rammichael.com/7-taskbar-tweaker-for-windows-10-october-2018-update/comment-page-1#comment-10200

I assume that 7+ Taskbar Tweaker v5.7 fixes that. If not, please leave a comment.

Thank you for the extensive feedback. The short story is that saving the taskbar state is tricky to do correctly, and it's a complex piece of code, maintenance of which would be extra work for me. On the other hand, not many users requested this feature, and it's not going to be activated often (exiting/launching/updating the tweaker, explorer/tweaker crash, which should be rare in a routine workflow. Any other cases?).

Given the above, I still am reluctant to add and maintain such functionality as a part of 7+ Taskbar Tweaker.

looking at some other feedback here RaMMicHaeL, I have saw you said 1 year ago "I might have a piece of code lying somewhere which can save and restore the taskbar items order. Let me know if it can help, and I'll check if I can find it."

I do have something - you can find it here as a part of the open source Virtuoz virtual desktop utility. If it will help, I can look at implementing a standalone tool to save and restore the taskbar state, e.g. via a hotkey or a timer.

You don't need to upgrade from Windows 7 to use the tweaker. Perhaps a new update of Windows 7 broke compatibility with the tweaker. If so, you're the first user to report it.

Could you please specify the version of your explorer.exe file?
Go to C:\Windows, right click on explorer.exe, choose properties, and go to details. What do you see in the File version field?

Also, can you look at the Windows Update history and see if you can track the update that causes the issue, perhaps by the date that the issue started happening?

Can you post a screenshot? Also, please provide more information: when does the issue happen? Does it happen only when the tweaker is running? Is there a specific option which triggers the issue? How can the issue be reproduced?

It's easy to check whether it's an issue of the tweaker. The "list" feature can be enabled via the registry. See this guide for example:

https://winaero.com/blog/taskbar-thumbnail-threshold-list-windows-10/

Set the tweaker to not run at startup, apply the "list" feature via the registry, restart (or exit the tweaker and restart explorer), and see whether you still see the issue.

I've just released v5.7.0.1 beta which should solve the issue. Please try it and let me know if it solves the issue for you.

By the way, I could reproduce the black window. It happens when you use the classic volume control.

Should be fixed in v5.6.2.4 beta. Please try it for a while, and let me know if the issue comes back.