I admit that I am not really involved into Solus - at least not as much as I would like - anymore. I am busy with other projects and personal life.
So the easy workaround is the following
- Do a full system update
- Reboot
- Launch Orache VM Virtualbox
- Files -> Check for update then follow the instructions
The key element is point 2.
Normally the usysconf trigger reload the virtualbox kernel modules (so the reboot shouldn't be required). There is most likely something to be improved there.
Just make sure to reboot your computer after virtualbox is updated and before trying to update the Extension Pack and you shouldn't face any problem.