Your work isn't being blocked.
This is typical behavior for all internet website forms -- an open connection can only be held open for so long.
To be technical about it -- HTTP protocols do not have any open connections at all, but merely only short page requests, GETs and PUTs. But sessions are defined on the server side to simulate open connections, so that the PUT request can be known as a proper response to the previous GET request. Webservers with limited resources, or that handle lots and lots of simultaneous requests can only afford to keep these sessions open for a short specified length of time. Else the entire site would be blocked to every other user. This is how DDOS (denial of service) attacks happen. One user makes many multiple requests, keeping them all open, so that no one else can access the site. Therefore, sessions are intentionally short.
As a workaround, copy the text into a local text editor, make your changes there, then paste it back into the website.
Its also okay to save your work frequently with multiple editing sessions.