VM changes from good to "inaccessible" after about a minute

[Stephen Rondeau]

With VirtualBox 6.1 on Fedora 30 and all updates applied, I create a VM and attach an existing virtual disk (Centos 7.6 is the guest operating system) as "immutable". I snapshot it twice afterwards, first to make a differencing disk image and next to allow students to roll back their changes. I have been doing this for nearly a decade across many VirtualBox releases, and it usually works. I can list the VMs associated with a user account:

VBoxManage list vms

and it will show the correct name of the VM for a minute or two of repeated "list vms", then it will change to "inaccessible".

When I revert to 5.2.34, this behavior goes away and the VM remains accessible and usable.