CalDAV Free/Busy Delay Issue

Hello, I’m a new member.

After upgrading Nextcloud to 15.0.5 I’m observing the following Issue.

  • In Thunderbird I open Developer Tools, Network Tab for request debugging
  • Create Event in Calendar overview
  • Invite Attendees

Now when Thunderbird is requesting Free/Busy data the request takes about 26 seconds for each contact requested (sometimes 44-50s). Before the upgrade, the response was reasonably fast, i.e. a couple hundred milliseconds. The response content looks the same as before. I’m not observing any significant CPU usage from PHP during those 26s. This only happens for free-busy data. Everything else is performing fine, including the Web UI, including calendar sync.

During the upgrade I’ve also switched from PHP 5.6 to PHP 7.3 and from modphp to PHP-FPM. Webserver is Apache, Debian Jessie, PHP 7.3 from, no proxy involved. Checked negative for RAM shortage.

Grateful for any ideas what to look after, double grateful for a ready solution.