Hello,
I think a couple of things went wrong here.  One was that the Chiltern Hills AONB had a gap in it.  You can just about see this at https://overpass-turbo.eu/s/1sRF (although that does join the gap up).  I've fixed that in https://www.openstreetmap.org/changeset/134103405 .
The other thing was that the school somehow got a "building" tag applied to the whole area.  I've removed that in https://www.openstreetmap.org/changeset/134103507 .
I hope this is all OK - any questions, please don't hesitate to ask.
Best Regards,
Andy
