CDF tracing shows that there is a timing issue and fhe ICA listener fails to create .Following errors are observed 

"CreateListener Listener on port 2598 already in use. Aborting incoming connection due to possible MITM attack"

"Failed to start Listener while preparing for connection. This will cause the connection to fail"

As a workaround disable EDT via Studio Policy . 

Then run gpupdate /force on the VDA and test again.

This will disable the UDP listener and listener creation process will be faster as only a TCP listener will be needed .

After upgrade from CVAD 2411 to 2503 VDA cannot launch desktops with error “Failed to retrieve ICA”