Hmmmm...
I just discovered that the zoom level od the site does not matter, it is changing the zoom level (up or down) that fixes the formating. The fix is only temporary for the current session. When closing the browswer and reopening it the formating is borked again, changing the page zoom (up or down) snaps the site in place.
This might be a bug for Safari in iOS and not the site. But this is the only site I have had problems with.