There is a content [Not displaying chat for certain amount of time] when the chat has ended.
This certain amount of time is, by default, it is set to be a day. (2019/11）
And this can be changed with the setting below.

(1)Click the setting button on the upper right of the management page.

(2)Click [Chat]>[Design]>[Menu] on the left side of the screen.

(3)Click [Menu]>[End] tab.

(4)Click [Display detailed setting]

(5)Enter number in the section "Not display for 〇minutes" in [Display [Not display chat for certain amount of time]].

(6)Click [Update]