@ambimom Is there any chance that pinch-zoom could have been triggered? On Mac, if you have "Zoom in or out" enabled in your Trackpad settings, that locally zooms the page content without changing the layout. It also doesn't change the Page Zoom indicator and does not get reset by the Page Zoom Reset (Command-0) action either.
Vivaldi on Mac also supports "Smart zoom" (if you have it enabled in your Mouse or Trackpad settings) that's activated with a double-tap gesture. This zoom/un-zoom function can also be used to negate/cancel pinch-zoom.