Disappearing check register entries

After all the Schwab interface problems, I thought my Quicken Deluxe, R37.67 on Windows 11, had stabilized, but yesterday I upgraded Quicken to Build 27.1.37.67 and today I ran an account update. My Schwab checking account balance jumped by $20,000! I find that is because many checks I have written in the past have disappeared from the register. For example, cleared checks 1900 through 1911 from 11/21 to 1/5/22 were all there yesterday; now the only checks from that list still in the register are #1900, 1905, 1907 and 1911. What is going on and how do I recover those lost debits which ought to be in my account? (I checked with Schwab Bank. All my missing debits are still in my register there, so my balance is much lower.)