I just wanted to say that I am having the same issues, and have been for at least a couple of months now. I haven't changed anything either, but have lost subscribed threads repeatedly, even after re-subscribing to them. My own journal has also disappeared many times from my userCP as well.
I like to click onto my user control panel and see all the threads all bolded, and catch up to threads I've been reading/posting to, plus all of my friends' journals as well.
Something went weird in there a couple of months back. I'd ask a question somewhere, and get seemingly no replies. Go back looking for the actual thread from the main forums days/weeks later, only to see that there
were replies. I felt foolish and wondered it I seemed rude for not replying back etc.
Thing was, I didn't know or see that anyone posted any replies to my question.
I was just reminded to finally speak up about this, because once again - I didn't see any updates to a friend's journal, and had to go looking/hunting for it, and found that there were posts - just that I don't see the updates anymore. Once again, I resubscribed to friend's journal (I've done that with several threads and have had to do it again and again sometimes).
I thought it was just me.