If you access the backend for a short period of time and then you are sign out, there could be a problem with allocated application pool memory for your account. If you reach the memory limit the application pool is recicled and you are sign out. There could be a problem with the authentication mode at the server level in the web.config. For instance if the following section is missing
It seems that the problem is related to your host server configuration, so the best solutuion here is to contact them and as what cause the behavior you experiance, since you are able to work the website without problems on your local server.
the Telerik team