RTÉ might possibly have discontinued the internet feed which the Radio Tuner app used. (The station would then still appear in the Radio Tuner directory but there'd be no data stream available for it to use).
The reason I suspect that's a possibility is because RTÉ (together with Ireland's independent broadcasters) launched their own app, funded by advertising, in April 2015 and they may be trying to make sure that you can't avoid hearing an ad when you first connect to the station.
The Irish Radioplayer app is here:
https://itunes.apple.com/ie/app/irish-radioplayer/id942453239?mt=8