Session lost after viewing device overview

When viewing a particular host (but this issue is not exclusive to this host), in most of the cases, the various graphs on the device overview page show "No Auth" in a pink image. When this happens, the session is destroyed and i need to log in again. This doesn't happen all the time, but it does most of the time. See attached image.
There's no indicator that it has to do with the limits specified in php.ini. There's no log entry in the error_log. The session just gets destroyed for no particular reason.