To clarify, we automatically don't unsubscribe users from your channel. We only remove spam subscribers. Also, have you noticed any unauthorized activity/changes made on your channel? If yes, keep us posted with specific details, we'll take a look.
YouTube doesn't automatically unsubscribe users. We'd recommend checking this Help Center article, under "Does YouTube automatically unsubscribe users from channels?" for various FAQs and to understand how subscribers work: https://goo.gl/1FsxZ2 . Hope this helps clarify.