OnAudioPlaybackPercent doesn't work after restarting the project

Using the OnAudioPlayback event in Blueprints does not work when playing the audio component its connected to while PIE, after restarting the project.

Tested in 4.20.3 (CL - 4369336), 4.21.2 (CL - 4753647), 4.22 (CL - 4932462)

1. Open a Blank Blueprint project
2. Import a WAV file, creating a SoundWave file
3. Right click the SoundWave and create a SoundCue from it
4. Create an Actor Blueprint class, named BP_Audio
5. Add an audio component to your BP_Audio Blueprint
6. With the audio component selected, add the created SoundCue to the Sound section
7. In the Event Graph, create an event instance of the audio component's OnAudioPlayback event
8. Have that OnAudioPlayback event execute a PrintString function, with its In String parameter being Playback Percent float output from the OnAudioPlayback event
9. Have the BeginPlay event execute the Play function on the audio component

Potential fix for OnAudioPlaybackPercent() always returning 0