Here's the "evidence" that the BT is coming and going. But I'm not sure how to make it clear that it's actually dropping completely out at the OS level and coming back on it's own...
Green line is hard-wired temp. Other three are Ruuvi tags. When they show, the Settings/Bluetooth menu shows up and the native BT is "Enabled." Also, when they show, the Settings/IO/Bluetooth Sensors menu is there.
But the only adapter seems to be the stock / built-in unit.
Then it'll all go away again - without touching / messing with it.