I used to be able to add a slice, and position it differently from one frame to another. This is very handy to create things like hitboxes. With Aseprite v1.3.18.1 or v1.3.17.2, if I create a new slice and try to do that, then the slice position seems to be shared across frames. Moving it on one frame moves it for all frames. If I modify an older slice (created with an older Aseprite), then it can still be positioned independently for each frame. So it’s like there’s a hidden slice configuration frame setting that triggers that different behavior (shared vs frame specific), and I can’t find it anywhere. It sounds like a bug to me.
I have reverted to v1.3.8.1, to get slices to behave the way I expect (I’ve picked this version randomly, it’s not necessarily the most recent one with this behavior).
Thank you.
Edit: so it turns out this is not a bug, but a deliberate behavior change to share slices across frames.
To restore the old behavior: Edit > Preferences > Guides & Slices > Prefer slice keyframes (obsolete behavior)