@rowan, have some unwelcome news: we have decided to revert the change above, so you will likely see this bug appear again if you re-publish.
The reason we are pulling the change is that removing
initial-scale=1 breaks the switch between portrait/landscape orientations on all iOS devices, so your customizations in Webflow between landscape/portrait don't work as intended. Instead, iOS devices load the initial version (e.g. portrait if you happen to load the site in portrait mode) and then scales it for the other orientation. So switching to landscape mode (wider screen) after loading in portrait shows a pixelated version that was intended for the narrower screen.
In other words, the change above breaks a lot more sites than it fixes. :\ Going back to the drawing board to figure out how to fix the
background-image: cover issue that you're seeing...
Currently, the only known workaround is to set
background-attachment: none; (not
fixed, so uncheck the Fixed option in Webflow), but that does affect the desktop resolution as well (since 'Tablet Portrait' has the same resolution as desktops).