Are you using KPN mobile? The Weerbericht app may not work.
Since the iOS 9.3 update problems are occurring for users who use the mobile network of KPN in the Netherlands. The Weerbericht app possibly cannot get new data when using KPN gprs, KPN 3G or KPN 4G.
FTP connection
The Weerbericht app uses FTP (instead of HTTP) to retrieve data from the KNMI. When using KPNs mobile network, the app cannot get this data.
Reported to KPN
We have reported the issues with FTP on the mobile network to KPN. In KPNs forum (Dutch) there is discussion about the subject. Hopefully KPN can fix this soon.
Info: KPN Forum