Any idea why?
Are you sure you did not forget to change the Audio setting in the System Settings from the usual HDMI output to the special Pulse Bluetooth output option, else of course you will get no bluetooth audio output and the audio will remain as before on your TV or AVR.
Can confirm Bluetooth audio works fine for me on my Bluetooth earpods with LE 8.2.5.1 on teh TX9 Pro S912 box.