When using Fiddler, there seems to be some bugs around resizing the GUI/UI, namely the dividers between sections such as between packet list vs. inspectors panes. It seems that when Fiddler is maximized full-screen, the divider (while using "Wide" layout) is shifted all the way up high, just beneath the initial packet in the list (Fiddler's update check).
I've been able to adjust the UI by manually manipulating Fiddler's registry settings, but even then it still seems finicky -- sometimes they take, sometimes they don't.
v5.0.20202.18177 for .NET 4.6.1
Built: Tuesday, April 14, 2020