The netcdf-out release configuration does not include the jna (Java Native Access) jar required by gt-netcdf for native linking.
We will need this on 2.9.x as well. Nice catch, Torben. It was only working for me with 2.9.x nightlies because I also installed the grib plugin, which includes the JNA jar.
Merged on master: https://github.com/geoserver/geoserver/pull/1648