STM32F746G Discovery Board UDP Comms not Working

I have a Simulink model running on a STM32F746G Disco board using the STM32 embedded coder support package. I wish to be able to control and monitor the Disco model target using a host Simulink model over UDP. The target model has UDP Send and UDP RCV blocks. The host model has model UDP Receive (HOST) and UDP Send (HOST) blocks. Host PC uses a USB to Ethernet adapter. There is no DHCP so static IP addresses are used on host 192.168.1.2 and target 192.168.1.3.

Matlab version is R2020b.

UDP comms from host to target works fine. However, the host does not receive any of the messages sent by the target.

I have tried the usual Firewall fixes of disabling the Firewall and adding custom UDP Port rules but none of these made any difference.

I have run a different model in PIL mode using TCP with the same static IP addresses and that works fine.

Is there anything obvious that I am missing or not setting up that is stopping the host seeing the UDP messages?