TFTR
I copied the error codes as-is, not retyped.
Bitlocker service is present and on Manual.
re: KB5000841 : KB4490628, KB4474419, KB4538483 are in place, but KB4575903 appears not to be – it was never offered in WU – now installed. KB4592510 was also in place (Jan 16); attempted reinstallation.
re: article: noted. Nothing extra there I think for action.
I shall now find out whether KB4575903 was the problem … using the standalone installer it appears to have succeeded (and according to Event Viewer, OK) – no reboot required.
The question is why that critical item was not installed?
(KB3133977 seems not to be relevant, given a bit more searching, so am giving up on trying that one for now, at least.)
Thanks indeed for helping resolve that.