OpenWSN on nrf52840dk: error with JRC

I want to use OpenWSN with RIOT. For this I followed the indication gived in the README in tests/pkg/openwsn.

For the leaf node, I did :

$ BOARD=nrf52840dk make all -j4
$ BOARD=nrf52840dk make flash-only
$ BOARD=nrf52840dk PORT=/dev/ttyACM1 make term

For the root node I did :

$ SERIAL=/dev/ttyACM0 USEMODULE+="openwsn_serial stdio_null" OPENSERIAL_BAUD=19200 BOARD=nrf52840dk make flash -j4
$ PORT=/dev/ttyACM0 BOARD=nrf52840dk BAUD=19200 make openv-termroot

For the leaf node, I got :

/home/maxime/Documents/Fac/M1/Stage/iCube/stage-icube/riot/RIOT/dist/tools/pyterm/pyterm -p "/dev/ttyACM1" -b "115200"  
Twisted not available, please install it if you want to use pyterm's JSON capabilities
2024-06-13 14:05:54,601 # Connect to serial port /dev/ttyACM1
Welcome to pyterm!
Type '/exit' to exit.
ifconfig
2024-06-13 14:05:58,223 # ifconfig
2024-06-13 14:05:58,226 # Iface  2  	HWaddr: 6B:4D  NID: CA:FE
2024-06-13 14:05:58,226 # 
2024-06-13 14:05:58,229 # 		Long HWaddr: 6A:F8:AD:63:4C:90:56:0F
2024-06-13 14:05:58,233 # 		inet6 addr: fe80::6af8:ad63:4c90:560f
2024-06-13 14:05:58,233 # 
2024-06-13 14:05:58,235 # 		IEEE802154E sync: 0
2024-06-13 14:05:58,236 # 		6TiSCH joined: 0
2024-06-13 14:05:58,237 # 
2024-06-13 14:05:58,238 # 		NO RPL parent

For the root node I got this after starting :

 ___                 _ _ _  ___  _ _ 
| . | ___  ___ ._ _ | | | |/ __>| \ |
| | || . \/ ._>| ' || | | |\__ \|   |
`___'|  _/\___.|_|_||__/_/ <___/|_\_|
     |_|                  openwsn.org

13:32:04 [OpenVisualizerServer:VERBOSE] loading logging configuration: /home/maxime/Documents/Fac/M1/Stage/iCube/stage-icube/riot/RIOT/tests/pkg/openwsn/bin/nrf52840dk/logging.conf
13:32:04 [OpenVisualizerServer:INFO] initializing OV Server with options:
	- log files directory     = /home/maxime/.cache/openvisualizer/log
	- data files directory    = /home/maxime/.local/share/openvisualizer
	- host address server     = localhost
	- port number server      = 9000
	- firmware path           = /home/maxime/Documents/Fac/M1/Stage/iCube/stage-icube/riot/RIOT/build/pkg/openwsn
	- set root                = /dev/ttyACM0
	- use page zero           = False
	- use VCD logger          = False
	- serial port mask        = ['/dev/ttyACM0']
	- baudrates to probe      = ['19200']
13:32:04 [MoteProbe:WARNING] Probing motes: ['/dev/ttyACM0'] at baudrates ['19200']
13:32:04 [MoteProbe:SUCCESS] Discovered serial-port(s): ['/dev/ttyACM0']
13:32:04 [OpenVisualizerServer:INFO] extracting firmware definitions.
13:32:04 [Utils:VERBOSE] extracting firmware component names
13:32:04 [Utils:VERBOSE] extracting firmware log descriptions.
13:32:04 [Utils:VERBOSE] extracting 6top return codes.
13:32:04 [Utils:VERBOSE] extracting 6top states.
13:32:04 [OpenVisualizerServer:INFO] Setting DAG root...
13:32:06 [OpenVisualizerServer:SUCCESS] Setting mote 5bc1 as root
13:32:06 [OpenVisualizerServer:INFO] starting RPC server
13:32:07 [RPL:INFO] registering DAGroot ae-86-97-28-d8-4b-77-ea

After a while I got these message :

13:33:05 [JRC:VERBOSE] New node: 6af8:ad63:4c90:560f. Creating new OSCORE context in /home/maxime/.local/share/openvisualizer/oscore_context_6af8ad634c90560f.json.
13:33:05 [JRC:VERBOSE] received JRC join request
13:38:01 [JRC:ERROR] Type-error in conversion of j��cL�V

It seems like the leaf node could not synchronize or join the network.

Does anyone have an idea where this problem could come from ?