In my dashboard I have few input to query SQL data or remote services and luckily I have faced this issue (rare) even after keeping my page idle for hours. in such case if I refresh the page web socket connection is reestablish and it works fine.
However there is already a open topic related to this issue. Cannot send data if the connection is not in the 'Connected' State
It points to web socket connection disconnection. You can check errors in developer tools (F12) and see if this is same issue you are facing.