Jul 12 17:54:41.968605 HTPC (uetoothd)[932]: bluetooth.service: Referenced but unset environment variable evaluates to an empty string: BLUEZ_ARGS, BLUEZ_DEBUG
^ This just means bluetooth.service https://github.com/LibreELEC/Libr…service#L10-L12 did not find either variable defined in the respective .conf files. It is harmless and if you check your own devices you will see the same boot time message.
If possible please test with another distro that uses a recent BlueZ version, and with a different BT dongle device.
If the issue occurs on another distro it's nothing specific to how LE has compiled BlueZ or a problem interaction between BlueZ and core OS functions in libc. If the issue remains with another BT device on LE it's either compile or something in the comms between the Soundbar and BlueZ. If the issue doesn't occur on other BT hardware, it suggests kernel driver or firmware.