Set the tempo to 50% or lower and play head scrubbing of audio track still works. As we keep working for some time, playhead scrubbing stops working at lower tempos - until the tempo is increased. Then again, it stops working at the newly increased tempo and we need to keep upping the tempo to make the scrubbing work.
Also, audio track playhead scrubbing stops working beyond a bar but it works before the bar at lower tempos after working on it for sometime. If we increase the tempo slightly, it works again but stops again after some time requiring to increment the tempo again.