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 to version 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).)
Boot on a kernel prior to 3.10.0-1062 e.g. 3.10.0-957
To boot on this kernel every time install the grub-optimizer - a graphical utility that enables you to edit the boot loader settings.
]$ sudo yum install grub-customizer
run it by typing
]$ sudo grub-customizer
Go to the General tab and select the wanted kernel to be default, e.g. 3.10.0-957.27.2
Click the Save button and reboot.
PS: Ultimo October 2019 with VirtualBox version 6.0.14 and the latest Centos kernels everything is again working correct.