DFPlayer Busy Output stuck at 2V

I have an existing proven design using DFplayer. Recently bought a new batch and found that they intermittently play tracks and bafflingly leave the BUSY signal (which I monitor) stuck at 2V. (rather than 3.3V or 0V). Has anyone else seen similar issues?

Where did you buy them? You may have received knockoff versions if you did not buy direct from DFRobot or DigiKey.

I bought them on AliExpress - I guess that is a lesson.