This is a different issue from cash positions in brokerage accounts.
The Fidelity Cash Management Account uses 3 separate positions for cash as they are all swept to FDIC protected accounts. This means that I see three separate cash positions in my account: QPCTQ, QPIAQ, QPIFQ. With the new Fidelity EWC+ connection, I have reset the Money Market securities / cash options in the Online Services tab and received the prompt to set one as the cash position.
But Quicken does not seem to be able to handle three different cash positions, or Fidelity is not sending the data correctly. It appears to have marked QPIAQ as my cash position but every time I update I get placeholder transactions for the other two. This did not happen with the Fidelity direct connect solution.
Note that this account is also set to "Show cash in a checking account".