What could be the reason she suddenly unfollowed me shortly after following me back?

Like I had been chatting with this girl for over a year on Instagram who used to be in the same school as me but didn't know each other in school days. the chats were infrequent as her replies were mostly delayed. She is 21 now and I turned 24 just 3 weeks ago. The chats has been neutral mostly but friendly too and the chats weren't even one sided and it has been more balanced. Today we shared about our hobbies and I said I cover songs on Smule and told her to follow me back if she is comfortable so she can watch stories of my singing. She followed me back and accepted my follow request and even viewed my Instagram stories which was a live concert of Your Love Is a Lie by Simple Plan but suddenly now I noticed she unfollowed me an hour after following me back so I am puzzled and wondering whether I should still continue chatting. What do you people think?