Need to understand why GRL test C_5_9_20 SSED is failing

[EricSTMicro]

Hello,

We are running a internal Openthread pre-certification, but we are struggling and running out of idea with only one test: C_5_9_20 SSED.

For an unknow reason, the DUT doesn't send a Child Update Request (in 802.15.4 v2015) at the end (and no ping), making the test to fail.

Please find enclosed the logs on a working platform (OTNCS12) and the failed on our platform (STM32): logs.zip

The logs provided have been tested on GRL v56.3.1, but the result is still the same with the last version v57.0.

Any ideas would be welcomed :)

BR,
Eric