F5 tcp connection per second limit

We have 10350 F5 model which we are running load-testing on them but somehow getting lost of connection failure when running load with 500k users with 800 per second connection rate, this is all port 80 so no SSL. i am getting connection failure on client side and F5 not telling me anything that its dropping connection and why?

is there anything related to DDoS protection or Syn attack threshold dropping connection? or F5 has any short of limit on connection per second rate. on VS i have all setting default.