If you’re using a session in the same browser as which you have a Gateway page open, the cookies will often clash, meaning as you log into one the other will eventually log you out. It’s not recommended to have Perspective sessions active in the same browser as an open Gateway page.
Additionally, Sessions will “refresh” whenever a Designer for the Gateway saves. If your sessions are open against a gateway that is undergoing active development, you should expect refreshes whenever someone saves their changes in the Designer.