Hey,
maybe it could be a good starting point to update the recent ownCloud Server 10.0.10 Release first before looking for issues in an outdated version?
According to a blog post i had read a few days ago it seems only the newer 10.0.10 version if fully compatible with PHP 7.2 you’re currently using. This could be related to your issue as you seems to be still on 10.0.9.