Hello there, ShivT,
There are different steps to fix mileage tracking issues in QuickBooks Self-Employed. Check this article for the detailed steps: Fix mileage tracking issues in QuickBooks Self-Employed for iOS.
As for the missing mileage trips, I recommend contacting our QBSE support. They will be ble to check your account and see what caused the error.
On your QBSE app, click on Assistant. Follow the next prompts to connect to our live agents.
Let me know if you have other questions.