If you have a bug to report, you do it here or by writing to our feedback address.
We can’t open Audacity Bugzilla to the general public because we don’t have the resources to manage the 95% non-bugs/already fixed bugs that would be reported (most of our users are on Windows, and there are a lot of Linux users on older versions of Audacity).
JACK issues are tracked here http://bugzilla.audacityteam.org/show_bug.cgi?id=56. Steve can comment when he sees this as he uses JACK, but Rescan is given as a workaround for connecting to newly added JACK ports, so it is not known that the Rescan crashes under JACK.
Clicking in the recording meter to start monitoring may crash Audacity if it has not yet used JACK for playback or recording in that session.
Does Rescan ever crash when JACK is not connected then you launch Audacity?