contiki-ng: Tutorial: TSCH and 6TiSCH - doesn't work

I followed the tutorial https://github.com/contiki-ng/contiki-ng/wiki/Tutorial:-TSCH-and-6TiSCH using two cc2650 devices. Unfortunately my not-coordinator device never gets associated. For the not-coordinator device I have the MAC logging enabled. I get the following output:

...
[INFO: TSCH      ] scanning on channel 15
[INFO: TSCH      ] scanning on channel 20
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 25␊
[INFO: TSCH      ] scanning on channel 25␊
[INFO: TSCH      ] scanning on channel 15␊
[INFO: TSCH      ] scanning on channel 25␊
[INFO: TSCH      ] scanning on channel 26␊
[INFO: TSCH      ] scanning on channel 25␊
[INFO: TSCH      ] scanning on channel 26␊
[INFO: TSCH      ] scanning on channel 25␊
[INFO: TSCH      ] scanning on channel 15␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 15␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 15␊
[INFO: TSCH      ] scanning on channel 15␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scan: received packet (24 bytes) on channel 20␊
[INFO: TSCH Pkt  ] ! parse_eb: frame is not a valid TSCH beacon. Frame version 2, type 1, FCF 41 e9␊
[INFO: TSCH Pkt  ] ! parse_eb: frame was from 0xabcd/0012.4b00.12b9.c702 to 0xabcd/ffff.0000.0000.0000␊
[ERR : TSCH      ] ! failed to parse EB (len 24)␊
[INFO: TSCH      ] scanning on channel 26␊
[INFO: TSCH      ] scanning on channel 20␊
[INFO: TSCH      ] scanning on channel 20␊
...

I assume that the that the EB is received because 0012.4b00.12b9.c702 is the address of my coordinator but something else is wrong.