FreeBSD-CURRENT VirtualBox guest: EFI: lost the ability to boot

[Graham Perrin]

With VirtualBox on an r368589 host I installed the latest (17th 
December) snapshot of 13.0-CURRENT in a guest machine. I set the guest 
to EFI before installation, and chose GPT (UEFI) during installation.

After installing KDE Plasma etc., the guest worked for a short while but 
then failed to boot. Screenshots at <https://imgur.com/a/xoYHwbT>; 
scroll down to 17:49:06 for a shot of a failure.

Is this maybe another case of bug 251866? 
<https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=251866>