When enabling slb directfwd on feature, TCP traffic will be blocked once APV use same port number of HA to establish connection with real service.
Port number is determined by the function fasttcp_find_open_port() after enabling directfwd feature, 

The issue is fixed by using function is_management_packet() to check current port number if it is used on other management features, such as ssh, webui, HA, etc.

configure a tcp real service
ha on
slb directfwd on
Try to let APV use the same port number of HA by constantly establishing TCP connection.