Possible root cause of the problem is Frappe 7.2 and ERPNext 7.2 being packaged there as of the moment (which is the way behind the latest 8.3 release codebase). Due to such a version diff, bench update runs into untrappable technical issues presumably.
This exposes certain limitations on those who would like to rapidly set up and evaluate the latest version of ERPNext in the local Virtual Box host environment.
Do you have any timeline as for re-building the Virtual Box VMs with ERPNext / Frappe 8.2 or 8.3 there?