I'm here to help you sort this out, @wrjohnston.
Let's start by manually updating the mileage tracking in your QuickBooks Self-Employed app on your mobile device. To do so, simply turn off the mileage tracking in your app by following the steps below:
- Go to Mileage.
- Select the Auto-tracking switch to turn it OFF.
- Click Sign out.
Once done, you can now go back and log in to your account then on again the mileage tracking. Here's an article for the detailed steps: Use automatic mileage tracking for QuickBooks Self-Employed.
If the issue persists, you may want to continue the troubleshooting in your mobile device. Depending on your mobile, I've listed the articles below for your reference:
Keep me posted in the comment section down below if you have any other questions. I'm always around happy to help.