I stupidly tought that the bootloader causes the problem... So flashing MM modem should be enough. Will try that, thanks!
Might be unnecessary, but I'd flash the whole modem stack and erase the settings, just to be on the safe side. Make sure every step is successful. Repeat if its not.
Code:
fastboot flash modem NON-HLOS.bin
fastboot erase modemst1
fastboot erase modemst2
fastboot flash fsg fsg.mbn
fastboot flash bluetooth BTFM.bin