UI response too slow

when I run the AG-UI langgraph project in Copilotsidebar, as the conversations because more and more, the UI display the messages also more and more slower, after 20 rounds of converstion. it needs more than 40 seconds to display the message after the agent finished generation. the words of each round of converstion not more than 100 words. it is unacceptable. how to short the response time of the process of UI? or somewhere i setting wrong or missing setting?
at the same time, the background will display a Error like:
[ui] Agent execution failed: TypeError: fetch failed
[ui] at ignore-listed frames {
[ui] [cause]: Error: read ECONNRESET
[ui] at ignore-listed frames {
[ui] errno: -4077,
[ui] code: 'ECONNRESET',
[ui] syscall: 'read'
[ui] }
[ui] }