Wi-SUN router join process fail (interoperability)

Hello everyone,

I have three setups :
-1 Border Router and 1 router node, both running mbed OS + nanostack with Wi-SUN :
OK : the joining process goes well, and after several minutes, I can ping my node through the BR

-1 Border Router Texas Instrument and 1 Router Node Texas Instrument :
OK : the demo runs fine

-1 BR Texas Instrument and the mbed-os router node : FAIL.

What I know/did :
-Network name are the same.
-Radio is good I can send/receive the frames and printf them on router node side
-Certificates on both router nodes are the same (so it should be recognized the same way by the BR??)
-I copied/pasted mbed_tls_config.h from Texas Instrument setup to mbed setup to be sure both mbed-tls setups are aligned

Is there something else I have to check?

Thank you for your help