Sometimes crashes when pressing Try again

[opk12]

Sometimes pressing Try again crashes the app.

FATAL EXCEPTION: main
Process: es.eoinrul.ecwt, PID: 10026
java.lang.RuntimeException: Unable to start activity ComponentInfo{es.eoinrul.ecwt/es.eoinrul.ecwt.TrainingActivity}: java.lang.UnsupportedOperationException: Cannot create AudioTrack
	[snip]
Caused by: java.lang.UnsupportedOperationException: Cannot create AudioTrack
	at android.media.AudioTrack$Builder.build(AudioTrack.java:776)
	at d.a.a.b.<init>()
	at es.eoinrul.ecwt.TrainingActivity.i()
	at es.eoinrul.ecwt.TrainingActivity.onCreate()
	[snip]

Version is 4.6 from F-droid, on Android 7.1.