REGRESSION: Yes, this does not occur in 4.17
When the user dismisses the right-click menu in the Content Browser, any active toasts will suddenly become hidden behind the editor window. Only when the toast updates will it appear above the editor again.
I wasn't able to reproduce this on Windows.
The toast is hidden behind the editor window.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-50771 in the post.