Maybe it would be helpful if when someone unsubs, a message would appear, asking the reason for leaving, and a few possible options listed to choose from.
And the creator would just get a notification saying something like "1 subscriber left due to: [insert reason here]" Doesn't have to say which person left.
Deviantart has that kind of system when I am deleting some of my art. Asks for the reason why I am deleting it, so that kind of thing is possible to code.