Not sure if this is the right place to be filing bug reports, but here goes!
How to reproduce:
- I have some bars in a specific time signature containing a rhythm slash region.
- Add a bar at the end
- Give that bar the time signature “open”
- Drag the end handle for the rhythm slash region into the new open time signature bar
- Dorico crashes, triggers OS X crash dialog
- Reload from auto-save!
Easy to workaround by creating a second rhythm slash region in the new open time signature bar so not blocking me.