Hello @ioan.stan
Community Document Server is the app developed by Nextcloud. With that said, we cannot guarantee stable functioning of this app and you have to contact Nextcloud support with detailed description of the problem.
Please see this: Community Document Server app in Nextcloud 18
If you want you can install official ONLYOFFICE Docs Community Edition on a dedicated server with this guide:
https://helpcenter.onlyoffice.com/installation/docs-community-index.aspx