A: For security, Pluto TV does not keep you logged into the web preferences panel forever. Your session may expire after a few weeks or if you clear your browser data. This is normal.
Note: If you are looking for a literal "my.pluto.tv.preferences" URL string, it is often an internal redirect. The user-facing destination is typically the "Edit Channels" tab found within your user profile dashboard. My.pluto.tv.preferences LINK