Reporting to see if this is part of:

  • Start, Action Center and notification toasts may at times have a background that is 100% transparent. A fix will be available in later flight for now, if you encounter this issue, try ending ShellExperienceHost.exe via Task Manager or rebooting to resolve the issue.

I don't think so, but ... Email received, clicking the notification icon in lower right, it opens and I don't see them from the mail app. Not a deal killer as the notification over the app itself pinned to the taskbar is there, and I would expect if it were just the background being transparent, that I would still see the text ...

Perhaps will be fixed on net build, other notifications are fine.