Yesterday @alep faced a similar issue with this PR: Fix httpd config for caldav & carddav urls by alepolidori · Pull Request #44 · NethServer/nethserver-nextcloud · GitHub
The problem is that you can’t have multiple DAV servers installed on the same virtualhosts which are using well-known CalDAV/CardDAV urls.
More info on well-known urls:
Currently, NS doesn’t have a mechanism to say something like “this software is my default DAV server provider”. Each application (WebTop, NextCloud and SOGo) must avoid to override the current configuration and break configured clients.
Maybe we can implement some sort of DAV handler where a software can register, then the user must choose what is its own DAV provider. But for a user is really hard to configure such technical thing.
The real fix, is to install only one CalDAV/CardDAV provider: choose your groupware an stick with it 
Because you’re removing a yum group.
Take a look at:
- De-install webproxy(squid) - #2 by giacomo
- Removing Web Proxy triggers removing a bunch of unrelated packages
- Software Center Package Removal Behaviour
Workaround:
yum remove nethserver-webtop5