Possibly due to a change of endpoint address/URL or the format of the XML content of that file - example here:

https://www.yr.no/place/New_Zealand/Auckland/Auckland/forecast.xml

the API for XML format is discussed here:

https://hjelp.yr.no/hc/no/articles/360009342833-V%C3%A6rvarsel-i-XML-format

I am seeing in the logfile that no data is returned:

2020-05-13 18:30:50 INFO XmlYrClient; Non-200 HTTP response from http://www.yr.no/placehttps://www.yr.no/place/New_Zealand/Auckland/Auckland/forecast.xml/forecast_hour_by_hour.xml: 404
2020-05-13 18:30:50 WARN XmlYrClient; Error reading Yr URL http://www.yr.no/placehttps://www.yr.no/place/New_Zealand/Auckland/Auckland/forecast.xml/forecast_hour_by_hour.xml: http://www.yr.no/placehttps://www.yr.no/place/New_Zealand/Auckland/Auckland/forecast.xml/forecast_hour_by_hour.xml
2020-05-13 18:30:50 INFO DatumDataSourceManagedLoggerJob; No data returned from [net.solarnetwork.node.weather.yr.YrWeatherDatumDataSource@59f7d5[LocationDatumDataSource proxy]]