Yes, relaunching calamares usually makes it crash, over and over.
This is old, but i admit i haven’t investigated it.
A hunch is that when closing calamares it becomes unable to unmount and remove the temporary files it creates, then finding some conflict on what is trying to do and the files that already exist.
The error doesn’t seem to appear if close calamares before mounting partitions, only after, that’s why my guess is related with it.
Weird thing you can manually unmount the partitions and even so calamares still crashes… Maybe try deleting it’s temporary stuff from /tmp folder, unmounting and then relaunch it, may work.
Another possibiblity is that some calamares background service is still enabled even if closed, so it can’t open again without crashing at some point…
One kind of test to be done is boot distros that also use calamares and see if this can be replicated, specially testing based and not based archlinux distros, this may help to find the origin of the issue.
Only my thoughts…