Agent stops relaying service response messages to DDS

After some amount of time the Agent can get itself into a state where it provides services, allows them to be called, forwards the messages onto to downstream micro but does not bridge the response back to the DDS

**To Reproduce**
Steps to reproduce the behaviour:
1. Run agent `ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyACM0 -v6`
2. Connect an MCU which provides a service
3. Run a node on the device which hosts the agent which calls the service in a tight loop
4. You will continue to see [==>> SER <<==] messages in the agent and logs in the MCU that the service call has been requested but no more [** <> **] agent messages
5. ros2 cli service calls will also hang from this point onwards
6. Restarting the agent gets everything back to normal

**Expected behaviour**
Agent should always bridge mcu to DDS and never need restarting

**System information (please complete the following information):**
- OS: Debian 11
- ROS 2 Humble and Iron
- Version 4.0.3 on iron branch