Usually that just means the server as a whole is slow, but your not logged in requests are being served from a cache.

Basically, a not logged in request can be answered with the same response for everyone, so the server generates the response once and then saves it to use over and over again. But, when you’re logged in the response is going to be slightly different for everyone. So the server has to go through the whole process of generating the page from scratch for your exact version of it.