I know the app used to allow for all connections in Ireland (eg Birmingham New Street to Cork via Dublin Port) but now will only show the connection to Dublin Port.
All the stations are still listed on the app - including Londonderry (on Android at least) - but won't show trains at all.
I'm not sure if it's a fault with the app as the website comes up with an error saying, "sorry, we don't have this information yet!", so there may be some connectivity problems with the Irish Rail/Iarnród Éireann and Translink Northern Ireland Railways live data feed.
Then again it can't find train times from Blackpool South to St Helen's Junction - it told us yesterday to go outward via Manchester Victoria then WALK to Manchester Oxford Road, and return via Liverpool Lime Street, Stafford and Preston! Seems to be a few errors in it.