Bluetooth disconnects

[Nachteule]

OMG

Haven't you long suspected that something is generally wrong with your system?
The various strange errors you report, that is really not normal

Have you used a different power supply in the meantime?

Kodi has nothing to do with Bluetooth, the message you see in the Kodi log comes from the Pulseaudio sink module.

When I use bluetooth, I always use the onboard module, I don't have an external dongle at all

If you want to see something in the syslog, you have to install a logger daemon additionally. I have rsyslog in use, because I log everything on a central logserver.