Asus chromebox bluetooth

This isn't a pressing issue, just curiosity mostly. I have a first-version Asus Chromebox converted to Linux, running Debian Buster. It has internal an internal bluetooth controller which previously worked. For various reasons I reinstalled Buster, and now the controller doesn't work, can't be detected, it's as if it just went poof. I attached a dongle, and that works fine, no issues at all. I've spent a few hours, off and on, searching for a solution or at least a reason, without success. Every bluez package available is installed. btmgmt doesn't see the internal controller, but does see and control the dongle. Using the dongle everything works as expected, but the internal controller is MIA. I can live with using the dongle, but I would be interested in knowing why the internal controller went away. I've looked inside, and can see no obvious defects, it all looks intact.