On March 22, 2019 the IRS announced additional relief for taxpayers who payed only between 80% and 85% of their tax liability. If your underpayment fell in that range and you filed before TurboTax was updated to reflect the additional relief, TurboTax might have calculated a penalty that you ultimately did not have to pay.
https://www.irs.gov/newsroom/irs-expands-penalty-waiver-for-those-whose-tax-withholding-and-estimate...
