
as attached, this shows what should happen when you hold your finger on a measure for a second or so. This is not happening?
(The color can be changed in Settings>Playback position.)
Check that Settings>Playback position is ON, then press play to start playback from the beginning of the song. Does each measure highlight as it plays?
You could force quit iReal Pro from the multitasking dock then tap to open it again, select a song then try a long press again.
If not, turn your device completely off, then restart, then test.
If you are still having problems, you will need to run a backup (in Settings), email to yourself (make sure it arrives), then delete the app, download from the App store again. You can check the long press on one of the exercise songs or import your backup songs to test.
Let us know any results, thanks.