It might be a one-off but for no apparent reason at all, anywhere between 1-5 of my 19 subscribed threads "decide" to drop their subscription* and this can be whether I post in one of the subscribed thread or not and if I do post in one of the subscribed threads, it can be either via my browser (Safari) or via the FT mobile app on my iPod.
*the latest thread to drop (which I have now re-subscribed) is
this one which dropped last night after I posted in it via the FT app