My site goes like this:

1. On Main page(a.do), Open pop-up with window.open()
2. On Main page(a.do), Submit b.do by targeting the pop-up
3. On Popup(b.do), Submit https://www.othersite.com(Not my site) by targeting self.
4. On popup(https://www.othersite.com), it returns to my site again(c.do) (I don't know exactly it returns to my site by submitting form or replace url)
5. On popup(c.do), Set some values to its opener(Main page, a.do)'s form.
6. On Main page(a.do), Submit the form

The problem is that my site's login sessions are often disconnected. Not always.

I don't know how other websites that pop up go to behave.

I'd like to know if what's happening on that site might affect my login session.

There is no chance of a session timeout because the time to visit other sites is very short.