Unfortunately (or fortunately, depending on your POV) this does not seem to be a FT site issue; unless this is happening to more members we have to assume it's a local issue at your browser/ISP/etc.

I'm wondering how you've been setting the subscriptions that are dropping off as opposed to the ones that are sticking with you -- differently? Are the ones that dropped ones that you set in FF versus Safari for the others or vice-versa? Or maybe even you set them through the app?