To update/upgrade or not to update/upgrade
The question is relevant when you have a environment that you want to keep stable.
Generally I recommend that you update your software - there are a lot of security updates as well as new functionality. But when running Centos in a virtualbox environment the security matters are less important. Therefore you can leave your system as is for a semester and update/upgrade in the break.
As of time of writing October 2019 there are problems with the combination of VirtualBox 6.0.10 and 6.0.12 and Centos 7.6 and 7.7.
If you downgrade your VirtualBox 6.0.8 and remember to install the extension pack for the version installed (e.g. 6.0.8) you should be able to get something working correct. (Also remember to install the extension pack in the guest (Centos).)