We're seeing the same thing in the wild. Security Scoped Bookmarks on macOS 15 don't resolve after a while. Reports are that a device restart helps, but only for a little while. Trying to gather more data from some pretty angry users right now... Same app/binary works on lower macOS versions. App is a sandboxed. Something is very broken resolving Security Scoped Bookmarks on Sequoia. Same error is indicated (256).

We're also seeing reports, actually, only a single report from a user experiencing the same issue on 15.1, but this is down massively from the vast influx of reports we had on 15.0, so I'm not 100% sure it's fixed but it's definitely improved from 15.0 I think. Also, I think this bug only affects sandboxed apps, sadly. Very hard for us to reproduce ourselves because even on 15.0 it took like 4-6 hours to get the error to appear... If you can reproduce this easily, worth filing another Feedback?