For me it wasn't that the slide doesn't stay in place (that much is expected), but that if you deviate from the path it immediately slips back to the beginning. That's a bit anti-pattern w.r.t. typical slides that either have a forgiveness zone around the element or update to the point on the slide nearest to the gesture point.

I think it is less intuitive to non-iOS users... Android has "swipe up to unlock" and there isn't really a UI element.

Uhm haha. On behalf of our community I would like to say that I was perfectly capable of understanding this mechanism thank you. Pretty sure the reason for the unintuitiveness for some people must rely on something else entirely.

iOS has been "swipe up to unlock" for some time now, as well as Android vendors had "slide to unlock" lockscreens earlier.

Android stock maybe. Android as delivered by various vendors? It depends. I've seen variations of this mechanism pop up - including ones requiring to keep the finger on the path or else you "lose the ball", and that one was in the phone UI, where you needed to swipe to accept or reject a call!

Not a ratchet, but an imaginary rubber band.