Hi nickthedogtrainer, thanks for reaching out to the Community
We're not aware of any current issues with missing mileage data in QuickBooks Self-Employed. Do you experience the same issue when viewing the mileage on both the app and web?
Additionally, please try exporting all trips (from the web, navigate to Reports > Mileage log > Set time range to All time > Click the drop-down beside View > Download to see if the trips show there.
