Due to a bug in the yum-cron/NsReleaseLock feature those who enabled the automated updates found a bad surprise today: their systems were updated to CentOS 7.6 by the daily cron job.
The NethServer 7.6 beta is still under testing/development, however some problems can be fixed by upgrading to it, as explained here: Unexpected (auto-)update to 7.6.1810
To avoid problems, I suggest to disable automated updates and review the updates manually expecially when upstream wants to release a new minor version.
For any doubt, wait for NethServer 7.6.1810 “final” to be ready.