When I try to launch the latest thumb version frim the stock calendar icon or from a widget it starts up and closes in less than a second. Using the Qalendar icon, it stays running, If I remove --background from the dbus call file, it works as expected but this reintroduces the unable to load ics file issue discussed upthread. With the --backgound switch reintroduced, tapping an ics file in the file manager opens the select calendar dialogue, but this too shuts before you can do anything with it.
killall qalendar; qalendar --background
I guess you still need to "killall qalendar" after upgrading, if you use the --background method. TBH I have gotten into the habit of rebooting if I update Qalendar. No issues to report here on non-thumb BTW