Owncloud tasks not syncing on iOS 13 (VS. Nexcloud tasks syncing very well)

Dear owncloud community,
I’m using Owncloud 10.2.1, Calendar 1.6.3 and Tasks 0.9.7. On iOS12, tasks sync fine. On iOS 13 tasks do not sync. Calendars do.
I’m using Nextcloud 16.0.4.1, Calendar 1.7.1 and Tasks 0.11.3 too. On iOS12, tasks sync fine. On iOS 13 tasks sync fine. Calendars too.
https is used.

Steps to reproduce

  1. Use Owncloud 10.2.1, Calendar 1.6.3 and Tasks 0.9.7 or Nextcloud 16.0.4.1, Calendar 1.7.1 and Tasks 0.11.3

  2. Use iDevice with iOS 12

  3. Set-up CalDav-Account with credentials given in Owncloud/Nextcloud Calendar.

  4. Tasks sync. Calendars sync.

  5. Use Owncloud 10.2.1, Calendar 1.6.3 and Tasks 0.9.7

  6. Use iDevice with iOS 13

  7. Set-up CalDav-Account with credentials given in Owncloud Calendar.

  8. Tasks do not sync. Calendars sync.

  9. Use Nextcloud 16.0.4.1, Calendar 1.7.1 and Tasks 0.11.3

  10. Use iDevice with iOS 13

  11. Set-up CalDav-Account with credentials given in Nextcloud Calendar.

  12. Tasks sync. Calendars sync.

Expected behaviour

Task should sync. Calendars should sync.

Actual behaviour

Tasks do not sync on iOS 13. Calendars do sync.

Server configuration

Operating system:

Web server: apache

Database: mysql

PHP version: latest

ownCloud version: (see ownCloud admin page) 10.2.1

Are you using encryption: no

Operating system: iOS