Alarm always plays default sound

When I try to set up an alarm using a custom sound - either a music track or a ringtone - it always plays the default sound. If I tap on "Sound" when editing an alarm, then choose "Pick from ringtones", I see a list of many ringtones, and by tapping on the triangle icon I can preview them correctly. But if I choose one, when the alarm time comes, I hear the default sound.

Nokia 735, Windows 1607, build 10.0.14393.1770

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