Schema registration fails while installing Nextcloud with UCS


I’m trying to install Nextcloud 17.0.2-0 with UCS 4.4-3. However I’m getting the following error while installing (copied from /var/log/univention.log):

[CRITICAL]: Registering schema file activaton failed: {u’kopanotest’: {u’ …} /usr/share/univention-appcenter/apps/nextcloud/nextcloud.schema failed
[WARNING]: Aborting …
[ DEBUG]: Calling remove

What causes this error? Other Apps like Dudle and Letsencrypt installed without problems.