1. Did you try running with and without this update in order to compare and to make sure it's the cause?
It's quite easy if you have a virtual environment, otherwise only uninstallation could help.
2. Are you sure there were no other changes to the OS or QVS configuration?
For instance, CPU performance strongly depends on memory slots/channels being used by QV applications. In case an application is loaded into a memory which is not dedicated for CPU than it will take longer time for calculation. Not so big as you mention, but this is the fact.
Please share you observations, it's very interesting.
Thanking you in advance.