Thanks for your response.
My W-2 does indeed correctly indicate a dependent care benefit of $5000 (in box 10) corresponding to our Dependent Care FSA contributions. I've also revisited the "Child and Dependent Care Credit" section of "Deductions and Credits". It correctly shows that we paid over $5000 to a childcare provider in 2019 and that my wife was not a full-time student and could care for herself.
It's still a total mystery as to why TurboTax thinks that we've forfeited $4700 of our DFSA contribution.
