It’s a known fault which has been reported but no permanent fix has yet been found.
A work around is to run the scan and when it fails click on “done” then rerun scan and it should work.
It does fail as it isn’t recorded in the scan history
But as has been said you can get round it by going through the process of starting a full scan twice, the second one should start
It has been somewhat random for the scan to work - it didn’t this am but having just turned my laptop on the scan did start properly.
It seems to affect some users only rather than across the board - probably why a proper fix hasn’t been provided yet.