I think when you perform the QuickBooks update as described in the post above (using the Help menu item Update QB) you must run QuickBooks as Administrator.  To accomplish this right-click on the QB program icon and choose "run as administrator".  You will need to enter your Administrator  password in the next window in order to continue.  Perform the QuickBooks update and then perform the Payroll Update again.  When I tried this and then re-opened QB with my usual login info the 941 form still did not populate the social security fields so I closed and opened QB choosing "run ad administrator" again.  Then the "PPP" message appeared on my homepage and when I tried the 941 form it worked properly.  I closed & re-opened with my usual user info and the 941 was still working properly.  I hope this helps.