The only reason I stick with Jeep through thick and thin is that my local Chrysler dealer has the most honest, professional and friendly service department I have ever dealt with. I have been a happy customer for over 20 years. The dealership is family-owned and the family patriarch was a mechanic, then a service manager at the location before buying the franchise. He knew all too well that you see a salesperson for one day but you have a long-term relationship with the service department.

It does seem that Manjaro is a tad more stable in VMs but if I want stability at all costs, I'll go with some form of Debian.

I cannot deduce an exact cause because I think it's a VM-Distro interaction. However VBox seems sensitive to corruption based on incomplete syncing of the Mirrors. All I know is that once I did a formal sort of both the Arch and EOS mirrorlists, the glitches went away. There doesn't appear to be the same problem with EOS on bare metal but I think I'll adopt the best practice of syncing before updating there as well. Why Arch is more of an issue than stable distros like MX also eludes me. But I think a rolling release is always more of a problem in VMS.

The one thing that I actually LIKE about Manjaro is the 2-week lag between Arch repos and Manjaro repos.  I can understand why someone who wants a cutting-edge distro would be turned off by that.  But for me, that is an extra layer of testing & fixes before it's released to Manjaro users.  I don't need a 24 or 48-hour turnaround for a fix to a package.  I'm absolutely willing to wait 2+/- weeks for the Arch users to get it sorted out and for Manjaro devs to ensure compatibility.  JMO...   OTOH....that IS an additional layer "away from" Arch.  Endeavour reminds me a little of Manjaro, but a few steps closer and drawing from the (mostly) same repos.

I'm glad you found a solution to maintain Endeavour as a VM on your system!  But now that we figured out HOW to make it work, I really wish we could figure out WHY it needs to be done that way?  I just don't know enough about Arch to even begin to guess?!