there is a possibility that they've unauthorized you or even blocked you to get you unsubbed. do you know if that could be the case? if you are on really good terms, then it could very well be a bug!
I don't know maybe it's just me but does anyone get a bug where you're suddenly unsubscribed (or worse, unauthorized) from a person? I came to check upon a good friend because I was worried that they weren't posting much as they used to, only to realized I unsubscribed and unauthorized them which is I never did in the first place