Of note, there's a new pre-built VM available (2.2.16) at
https://github.com/BitCurator/bitcurator-distro/wiki/Releases that you may wish to try. The older 2.2.8 VM and the new release have been retested and tested respectively on a selection of hosts (Windows 10, Windows 11 beta, macOS 11.2, and Ubuntu 18.04/20.04) in Virtualbox 6.1.26 with the 6.1.26 Extension Pack installed and with 4GB RAM and 2 processors assigned.
A few other thoughts in addition to Euan's suggestion. Issues like reported CPU lockups in the VM can sometimes happen when VirtualBox itself is damaged. Removing and reinstalling is a good idea if you haven't already tried it, along with ensuring the latest VirtualBox and VirtualBox Extension Pack are installed, and that the latest Windows updates (or at least, the latest available to you if you're on an Enterprise license) are in place.
It may also help to bring up the Windows Task Manager on the host on startup to see which applications or background processes (aside from VirtualBox) are using a lot of processor or memory. Sometimes errant antivirus scans, enterprise management apps, or other 3rd party tools can lead to degraded behavior.
The new 2.2.16 VM has many core OS updates and is running the latest (6.1.26) VirtualBox guest extensions, so that may also help if none of the above does.
Kam