5–10% monthly growth is solid for an established channel. 20%+ is exceptional. New channels often see faster percentage growth because the base is smaller.
Unfollows happen when content quality drops, posting becomes inconsistent, or your content shifts away from what your audience followed you for. Platform purges of fake accounts also cause sudden drops.
This varies wildly by niche and platform. On YouTube, 50–200 subscribers per video is healthy for small channels. On TikTok, a viral video can add thousands overnight.