Strange behavior with scrolling tabs and tab separation bar

  To begin with, this line that delineates the tabs from the toolbar-it's great and without it Edge becomes a low contrast eyesore. Lately when I start up Edge dev, RANDOMLY this line will disappear, it's very frustrating. Sometimes restarting Edge fixes it, sometimes it doesn't.

Finally, I cannot get scrolling tabs to work-I want them as it's otherwise unacceptable how the Close Tab button disappears when I have ~15 or more tabs open (the little x). I tried adding this command line to the Edge Dev shortcut: " --enable-features=ScrollableTabStrip:minTabWidth/100,ScrollableTabStripButtons"

But it does nothing. Thank you for your help!