So, after a lot of comparing the commits between OE and LE without finding anything helpfull I started a shot in the dark and replaced the bootloader and dtb files from LE with the one from OE, and Bluetooth started working. So I did a binary compare and found that the only file that differs between OE and LE is "bcm2710-rpi-3-b.dtb". So something is wrong with the bcm2710-rpi-3-b.dtb file used by LE.
As a workaround you can download the OE 7 beta tar file, extract the bcm2710-rpi-3-b.dtb from it's "3rdparty/bootloader" directory and replace the one on the SD card with it.