As I realised later, fimware flashing repeatedly failed due to a dead battery. And I had no means to find out since I had removed BME and the charging mechanism was badly broken. Eventually used an external battery to charge, and flash.

Did take about 8 samples with both powertop and zzztop and the general pattern remains the same. Does so even after flashing.

I bought the device used (and fairly battered) and as someone in a different thread pointed out, aggressive overclocking *may have* led to BT failure in their case [1]. Could well be the case here as well. My worst fear is that the device may be dying.

Thank you.

[1] - Possible but unlikely, as I've come to understand from subsequent posts in this thread.