Classifieds uses the same integration file as Photopost and Reviewpost so I dont see an issue there.
I am just stating what I tell every customer when they post cookie settings as you have posted.
If you want users to be logged in they must be cookied in and the cookie settings must be exact. Therefore a domain of .domain.com is warranted.
Also please realize all of our products within the last couple months now only work with phpBB 2.018 and above so if your using a new classifieds and an old phpBB this could be an issue for you.