I have a report connected to a PBI dataset using live connection and am finding that the date formatting in the "child" report doesn't match the formatting applied to the field in the dataset. This issue has been reported repeatedly in the Issues forum by other PBI users as far back as 2019 from my search, but the issue is STILL happening as of 2022.
It's a ribbon UI bug only, you will still see the actual data in visuals formatted as expected. The product group has filed this UI bug and they will fix this issue in the future. Currently, no expected available fix time for it. Thanks for your understanding!