MacBook Pro Retina 15 inch mid-2015 model turns its bluetooth off by itself

Hi there,

I was using a bluetooth keyboard and mouse set on my MacBook Pro (Big Sur 11.1). Both worked fine, until, recently, the two devices could not wake up my MacBook Pro any longer. So I tried to wake up the computer by using the built-in keyboard, and it worked.

Then I checked the bluetooth in System Preferences. It reported that the bluetooth is turned off???Nevertheless, I can tell that I never turned the bluetooth off, and this has happened for twice.

Does anyone have a clue on this?

Regards,