Although Quicken closed the discussion having this title, this is a bona fide problem. While all my accounts seem to update properly, several were missing from the Update Summary panel when it completes. This is even the case if I perform an update from within a single affected account (from the download panel) — after completing, a blank summary screen pops up.
For me, deleting a "runtime.dat" file located at C:\ProgramData\Quicken\Inet\M**** worked for me. (M*** is a folder named using the first 9 letters from my Quicken data file name.) This corrected the problem for me and missing account have re-appeared in the Summary.
Quicken needs to investigate this problem because it is a bona fide bug. The problem apparently revolves around the application's manipulation of the "runtime.dat" file (and possibly others).