SUMMARY
KAlarm constantly deactivates its active calendar,
so you can neither save a new events nor display existing ones!

STEPS TO REPRODUCE
1. Start KAlarm (main window) 

OBSERVED RESULT
* "Active Alarms" is deactivated (even if it had been been manually reactivated during last session)
* No alarms due are displayed (This being very fatal for people who do not notice the malfunction of their calendar!)
* No new appointment can be created; if you try from command line (/usr/bin/kalarm --edit-new-display), the message "You must select a calendar to save the alarm in" is given.
* As long as you do not try to enter a new date, you will probably not even notice the condition.


EXPECTED RESULT
* "Active Alarms" are active (and remain so between sessions)
* New events can be scheduled
* Existing alarms are displayed in time
an in addition, ideally:
* In case of a malfunction of the calendar backend at least the user should be warned! (A running kalarm process with no active calendar is likely a malcondition.)

SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.20
KDE Plasma Version: 5.20.0
KDE Frameworks Version: 5.75.0
KAlarm Version 3.0.2 (KDE Apps 20.08.2)
Qt Version: 5.15.0
Kernel Version: 5.6.0-1028-oem
OS Type: 64-bit

ADDITIONAL INFORMATION
* In contrast to bug_id=423043, there is no duplicated entry for "Active Alarms", and manual (re)activation works normally
* The described malfunction occurred in KDE Neon (Ubuntu 120.04 based) about 1-2 weeks ago (due to the "quietly creeping" nature of the error, no exact date can be given).
* Severity level is grave, because reliable reminding of appointments is the main function of a calendar.
* As a workaround, at least a command line / dbus / ... equivalent to automate the manual reactivation (as an after-logon-sript component) would be helpful for the meantime