On a fresh day, I came to this post about extracting Contact and Calendar from database directly: Calcardbackup: bash script to backup Nextcloud calendars and addressbooks as *.ics/*.vcf files
If this handy tool can extract the table from database, at least it means the tables are in fact all good and not corrupted.
It did! It extracted all successfully:
$ sudo -u www-data ./calcardbackup "/var/www/nextcloud"
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+
+ Sat 10 Jun 2023 08:26:28 AM CST --> START calcardbackup ver. 5.2.0 (22.03.2023), AGPL-3.0
+ Checking dependencies and preparing...
+ no usersfile given:
+ - will fetch all available items from database
+ Using URL: https://nextcloudpi
+ can't read status.php (cURL code '60').
+ Nextcloud 26.0.1 detected.
+ Database of chosen Nextcloud installation is MySQL/MariaDB.
+ Looking for calendars in your Nextcloud:
+ Saving calendar ncp-Personal.ics......empty calendar!
+ Saving calendar aaaa-Personal.ics......success!
+ Saving calendar bbbb-Personal.ics......success!
+ Saving calendar cccc-Personal.ics......empty calendar!
+ Saving calendar dddd-Personal.ics......success!
+ Saving calendar eeee-Personal.ics......empty calendar!
+ Saving calendar ffff-Personal.ics......empty calendar!
+ Looking for calendarsubscriptions in your Nextcloud:
+ No calendarsubscriptions found.
+ Looking for addressbooks in your Nextcloud:
+ Saving addressbook ncp-Contacts.vcf......empty addressbook!
+ Saving addressbook aaaa-Contacts.vcf......success!
+ Saving addressbook bbbb-Contacts.vcf......success!
+ Saving addressbook cccc-Contacts.vcf......success!
+ Saving addressbook dddd-Contacts.vcf......success!
+ Saving addressbook eeee-Contacts.vcf......success!
+ Saving addressbook ffff-Contacts.vcf......empty addressbook!
+ removing temporary files...
+ Compressing backup as *.tar.gz file. Be patient - this may take a while.
+ Backup successfully compressed!
+ Find your compressed backup here: /home/pi/calcardbackup/backups/calcardbackup-2023-06-10.tar.gz
+ Sat 10 Jun 2023 08:26:41 AM CST --> END calcardbackup
+
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+ Support the developer: https://codeberg.org/BernieO/calcardbackup#donations
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This leads to think towards a permission problem as you said as no actual data nor table were corrupted.
Then I set to ncp-config to address those:
$ sudo ncp-config
Cannot load Zend OPcache - it was already loaded
Running clear-php-opcache
Clearing opcache...
Done.
Done. Press any key...
Cannot load Zend OPcache - it was already loaded
Running nc-fix-permissions
Cannot load Zend OPcache - it was already loaded
fixing permissions in /mnt/ncdata/data... done
Done. Press any key...
Then I logged into the Web view. It works now, for every member!.
Hence I guess during the error of Calendar update, it messed the permission somehow, which caused the trouble.
Thank you for the feedback and let me know this is not an isolated case. I wish the App developer would be aware of this.