In the compare view, the source editor cells and notebook content can become misaligned when the width of the window changes enough to cause lines to wrap differently.
Here’s an example, try starting with a wide window and shrinking it until the header line “Fork = Change text input value using result from click interaction with a Leaflet map by Bryan Gin-ge Chen” becomes two lines. The Leaflet cell becomes obscured by the source.
Long code lines in the source cells can also trigger this: