FYI: I have RM 18.104.22.16829 installed.
After two errors during the transfer process (and my retrying) the third attempt completed the download and transfer process and reached the "Applying Software Update. This might take a few minutes."
Nothing was happening for at least eight minutes, and the Cancel option was greyed out.
Patience. I was about to try to terminate what appeared to be a permanent update stall (the update process never starting) when the profiler screen did finally indicate "Updating PROFILER".
The Update completed and KPA restarted. All is A-OK it seems.