So what happened:
Had a board sitting on the shelf for half of a year. I took everything apart and reassembled it new, checked battery and rewired most of the connections. Everything was ready, but i didn´t connect the motors to the vescs (4.12). To test the new lights i switched on the BMS to power the vescs which feed the leds through the receiver. Both Vescs are powered on the same time and are connected over CAN. Plopp! Bit of magic smoke and no LEDs on on both Vescs. Reciever was still powered and Lights worked like they should. After i closed my WTF-face a minute later i checked the Can cable. Everything good! Nothing loose and not a bad contact!
HOW did i kill them? Had a propper connection, both vescs were powered and firmware was configured the right way about half a year ago and can worked back then!