>I don't understand what you mean by "reset of new messages". Could you please explain?

New messages appear when you log in or when you manually refresh.

If you believe someone else is using your account, you may change your password.

Otherwise, it may well be that you are not even hitting our server on some hits. Make sure you are hitting the server on every hit (browser setting in regards to cache issue) and that you don't have a proxy which is badly configured which would result in the same situation.