I think the problem is with ACPI, not OpenRC's savecache itself.
With the old GhostBSD 19.09 even when successfully upgraded to 19.10 it still doesn't show additional information after Saving dependencies cache... I deleted the savecache server, the boot time seems to be a bit slower and shutdown a bit faster. So I think it doesn't worth to delete savecache, just keep it as is.
I downloaded GhostBSD 19.10 and did a fresh installation. This version does show additional information after Saving dependencies cache... This information really provide more insight into the problem.
I observed that it really done everything properly but finally dropped into a system halt instead of poweroff. This symptom is the same as on Linux some years ago