All the roads and features were enabled and disabling and reenabling then didn't help.
It's happened several times before, both on the iPad and on my Android phone.
When it happens again I'll try to get a screen shot but it's rather as is only the first few layers of information is shown.
Hannah suggested deleting the map and reloading it and that works but requires an internet connection. Another way seems to be to power off the iPad, then restart it and SD.
I found that the airfield specific circuit diagram and noise sensitive areas were also not displayed.