to save battery life, iPad OS is aggressive about shutdown network access to background processes (minimized). Normally an app has to request background network access. This will allow it to make periodic access, but not allow a continuous connection.
the RD app does not ask for background permission, probably because the protocol is designed for persistent connection. a quick connection, then disconnect is not much use in the background.
in short, if the RD goes background, after some time the connection will be closed by the O/S and when it comes to the foreground, a reconnect is required.