Compared properties based on session is a very bad thing. The session is not stable and sometimes it last only for few minutes.
It was working perfectly when the compared properties were based on cookies.
You should leave at least in configuration that people can choose whether they would use cookie or session.
When the compared properties were based on cookie people could come back on the website after 6 months and their favorite properties would be still hanging there in compared properties. Shame that it doesn't work anymore.
