help, how can i send Send server message to clients

A tcp server that communicates with multiple clients.
I use a dictionary for storage when the client connects for the first time. Key==ip address and port, value==chanel instance
I found that the client can send information to the server in time.
The problem is that the message sent by the server to the client will be slower and slower and eventually will not be completely received.
The maximum delay can exceed 10 minutes.
Usually with such a huge delay, the message sent by the client to the server is not received by the server.

I am very surprised, I don't know what went wrong. Then, using the bs architecture request feedback mode, this problem still occurs. This can at least rule out the problem that I may use to store the chanel in the dictionary.

The original client is the unity engine program, the server side of the console. Later changed to all consoles, still have this problem.

The operating environment is windows10, vs2017. net frameworkVersion 4.6 or 4.7

I searched the Internet for a moment, and no one seems to have encountered this problem. So take the liberty to ask where the problem might be.