[Bug] [TC-CNET-4.12] Timeout at Step 8 – TH unable to communicate with DUT on THREAD_2ND_OPERATIONALDATASET (Python inside Docker)

Describe the bug

The test case TC-CNET-4.12 is failing at Step 8 due to a timeout when running the Python test inside Docker.

At Step 7, the 2nd Thread network is connected with the DUT. After this step, the Test Harness (TH) is unable to communicate with the DUT.
As a result, at Step 8, where TH discovers and connects to DUT on the PIXIT.CNET.THREAD_2ND_OPERATIONALDATASET operational network, the test fails with a timeout error.

Steps to reproduce the behavior

1. Manually Create a OTBR network-1 with the following commands:

• sudo docker network create --ipv6 --subnet fd11:db8:1::/64 -o com.docker.network.bridge.name=otbr0 otbr
• sudo sysctl net.ipv6.conf.otbr0.accept_ra_rt_info_max_plen=128
• sudo sysctl net.ipv6.conf.otbr0.accept_ra=2
• sudo docker run -it --rm --privileged --network otbr -p 8080:80 --sysctl "net.ipv6.conf.all.disable_ipv6=0 net.ipv6.conf.all.forwarding=1" --name otbr -e NAT64=0 --volume /dev/ttyACM0:/dev/ttyACM0 nrfconnect/otbr:9185bda --radio-url spinel+hdlc+uart:///dev/ttyACM0
  To get the hex values: docker exec -ti otbr ot-ctl dataset active -x

2. Manually Create a OTBR network-2 with the following commands:

• sudo docker network create --ipv6 --subnet fd11:db9:1::/64 -o com.docker.network.bridge.name=otbr20 otbr2
• sudo sysctl net.ipv6.conf.otbr20.accept_ra_rt_info_max_plen=128
• sudo sysctl net.ipv6.conf.otbr20.accept_ra=2
• sudo docker run -it --rm --privileged --network otbr2 -p 8081:80 --sysctl "net.ipv6.conf.all.disable_ipv6=0 net.ipv6.conf.all.forwarding=1" --name otbr_2 -e NAT64=0 --volume /dev/ttyACM1:/dev/ttyACM1 nrfconnect/otbr:9185bda --radio-url spinel+hdlc+uart:///dev/ttyACM1
  To get the hex values: docker exec -ti otbr_2 ot-ctl dataset active -x

3. Run this command in the RPI's terminal to open the docker:
   docker run -v /var/credentials:/credentials -v /var/run/dbus/system_bus_socket:/var/run/dbus/system_bus_socket -v /home/ubuntu/certification-tool/backend/test_collections/matter/sdk_tests/sdk_checkout/python_testing:/root/python_testing -v $(pwd):/launch_dir --privileged --network host -it connectedhomeip/chip-cert-bins:f902839abf1de0d17956de34889b6ad997e2c5e4
4. Python scripts are available in the following path inside the Docker container, Please navigate to this path to access the scripts: cd /root/python_testing/scripts/sdk
5. Make sure the DUT is advertising. (QA has used nRF52840-DK board as DUT)
6. Commands to execute the TC(Python Scripts) inside the Docker container:
   python3 TC_CNET_4_12.py --commissioning-method ble-thread -d <discriminator> -p 20202021 --thread-dataset-hex <thread-data-set_1> --string-arg PIXIT.CNET.THREAD_2ND_OPERATIONALDATASET:<thread-data-set_2> --endpoint 0

Expected behavior

The test case should be run completely and PASS without any issues.

Log files

Controller Log for reference:

• TC-CNET-4_12-PythonInsideDocker-Failure_log.txt

DUT log for reference:

• TC-CNET-4_12-PythonInsideDocker-Failure-DUT_log.txt

Environment

TH Version: v2.14-beta3+fall2025
Sha: 24f227f

Additional Information

During 1.5TE2, this test case is passed in the Python Inside Docker.
Reference Controller Log: TC-CNET-4_12_PythonInsideDocker_Log.txt

Environment:
TH Version: v2.14-beta2.1+fall2025
Sha: ddb4b4f