Why are my downloaded Charles Schwab IRA accounts balances consistently incorrect?

Whenever I update my accounts for my Charles Schwab IRA accounts on Quicken for Mac, it consistently results in incorrect data. This is evident in duplicate securities, missing securities, and securities that are no longer in that IRA account. I have welcomed the chance to monitor my investments in one place, as Quicken is supposed to allow me, but it is frustrating to never have confidence in the numbers it provides.