I remembered something about VirtualBox not playing nicely with Hyper-V on Windows, and dug up a possibly relevant post[0] on their forums. IIRC we ended up moving a few build systems to Docker and dropping VirtualBox because of hyper-v related issues, but it's been a few years.
That's the unrelated green-turtle issue. It's only relevant after the guest has actually started running instructions. I'm talking about before that point.
I'm not aware of any turtles, that was just the first thing I found when trying to see if VirtualBox and Hyper-V were still a problematic combo.
Again, it was a few years ago, but we didn't solve the problem or identify an actual root cause. We stopped banging our heads against that particular wall and switched technologies.
[0] https://forums.virtualbox.org/viewtopic.php?t=112113