TCP843 Flashplayer24

I'm in trouble about web application related to Flash player.

I had used this application in IE10 /Flashplayer21, and it had worked normally.

But when I updated to Flashpleyer24 in December 2016, I couldn’t login to application.

I investigated it with Wireshark. The following is current situation.

・This application uses flash, and connects client and server. （TCP:843）

　http://www.speedguide.net/port.php?port=843

・But TCP843 had been closed by the firewall in the specific environment where now I face problem.

・When I use flash21, I tried connect to TCP843 and failed 2 times. After that, I think maybe it could connect another methods.

・When I use flash24, I tried connect to TCP843 and failed 5 times. Now I cannot login.

-Supplementation

・When I couldn’t login, displayed the error that no login allowed.

   But actually I failed before be authenticate by server.

・I tried the packet that isn’t closed TCP843, and I can exchange using TCP843

  between client and server in this environment. I can login normally.

-Question

Could you tell me if you know like a following change?

⇒If it isn’t possible to use port or TCP843 in the flash21 and later,
   flash used another port, but ver22 and later removed that system.

Could you tell me if you have another hints or information related to this case?

I think if I open TCP843, this problem solve. But I would like to know the reason this problem happen when I updated ver24.

With best regards