The issue seems to be because the editor has been moved to an "undocked state". Thus, every file now opens as a separate window instead of opening in MATLAB editor.
The editor can be reverted to "docked state" by opening "Show Editor Actions" options on top right of any editor file and choosing "Dock All in Editor". Alternatively, you may use "Ctrl+Shift+D" keyboard shortcut to dock editor back to MATLAB.
