Hi there Julian_Haupt,
thank you for your reply !
You made me realize that the only reason why the second attempt to install the Aug SUv1 via Windows Update did complete without issues via Windows Update after rolling back the VM last week is the helper "Network Service" dummy account we created when trying to use the workaround to install the original release was already there. In fact, I manually removed it after the second attempt to install the Aug SUv1 completed successfully.
This explains why the attempt to install the Aug SUv2 fails as the dummy account does not exist anymore.
I confirm I will proceed with the action plan as suggested.
Thanks !
Massimiliano