Ok, so the exact same thing just happened again. Went to bed last night and this morning there is a Radeon Software Installer "Error 186 - AMD installer cannot continue due to missing or corrupted manifest files".
At least this time there IS an update available 21.6.1 -- 21.6.2. That said, I've looked at what 21.6.2 does and decided it's not worth getting.
I have to stress that I DON'T want the drivers to autoupdate. I don't mind being notified there are new drivers but I want a chance to see what they fix (and break) before installing them.
Why is it trying to do an install when I have autoupdate turned off?
How do I stop it trying to do autoupdates?
edit: Oh, and it appears to have now broken my existing install as I can no longer start the Radeon software to change settings or monitor performance. Just great...