I am not surprised in the slightest.
On a little tangent: my work laptop recently updated and the entire thing was going swimmingly (well aside from the fact Windows needs to restart 3 times in order to "Update and Shutdown" but eh) up until it got to 100%. The time it took to get from 0% to 100% was less than from 100% to actually finishing. I had enough time to hypothesize they let AI change something in the update process and one condition was to not increase how long it took to "complete" the update, ie get to 100%.

