UPDATE! I figured out the problem. All expenses or income must be categorized in an Account that is NOT an Asset - they must be either Expenses, Cost of Goods, etc. Intuit techs could not figure this out during an hour-long chat session, but I noticed that all my expenses in the Transaction tab were categorized as Current Assets rather than an expense, so QBO would not add those transactions to the Projects Income + Expenses = Profit summary.

Hope this helps anyone else who has run into this issue.