Hello,
I’ve had the same problem. For me it occured when I imported a quicktime movie (with audio) that was rendered in After Effects. Suddenly no audio would play out of Premiere at all and I had to re-import the old project into a new one to get things working again. Restarting Premiere and the system made no difference which makes me think this is a Premiere issue rather than a Quicktime one.
Perhaps it could be related to this “conforming audio” process that Premiere seems obsessed with??
c