Facebook friend blocked me for no reason?

[Robin]

There's this friend I meet up with now and again along with a few other people in the same friend circle and we were mid way through arranging another meet up. Then out of no where she blocked me, without any arguments or even anything that could be easily misunderstood.

I logged in with my musician's account to check she hadn't just deactivated her account but her account was there and open. The only thing I can think of it being is her also being friends with my ex so maybe she had something to do with it but then someone else in my friend circle is also friends with my ex and she's still fine being my friend. Why would she have blocked me?