The auto mileage tracking no longer works on the iPhone 13 pro max. Tried switching it off and back on.. seems to work intermittently if you drive with the app open

Let's perform some troubleshooting steps to get your auto mileage tracking working, simon52. 

I appreciate you for performing some troubleshooting solutions to get your auto mileage tracking works on your iPhone 13 Pro max. We can try refreshing the application to eliminates common issues that cause your mileage auto-tracking not to work. This can be done by clearing the app's data.

For QuickBooks Online app, click the menu at the top right and choose Settings. Then tap Refresh Data and choose Yes. In your Phone Settings, select Apps (varies by device). Then, choose the QuickBooks app from the list and select Storage and tap clear data. Then, review the general location settings on your phone or tablet. Let's make sure the QuickBooks mobile app can run in the background. If you don't let the app run in the background, it only tracks trips when it's open and active on your screen. On iOS (iPhone and iPad), follow the steps below: 

1. Go to your iPhone or iPad's Settings.
2. Scroll down and tap the QuickBooks app.
3. Select Location. Then click Always.
4. Turn on the Motion & Fitness, Background App Refresh, and Cellular Data options.
5. Close your settings.
6. If you see a message about background location use, select Always Allow. Don’t select the While Using the App, or Only While Using options. These prevent the app from tracking your mileage consistently.

Your device and app are now set up to track trips in the background. Switching to a different app shouldn't interrupt mileage tracking. If your device is connected to a Wi-Fi hotspot while you’re driving, this can interfere with recording the trip accurately. Wi-Fi can be turned on but make sure it's not connected to a hotspot while driving. It’s also OK to have Wi-Fi on in your location accuracy settings. For other troubleshooting steps, check out the Fix mileage tracking issues in the QuickBooks Online mobile app article. 

Feel free to visit our Help Article page for more insights about managing your business in QuickBooks. 

I'd like to know how you get on after trying the steps, as I want to ensure this is resolved for you. Just reply to this post and I'll get back to you. You have a good one.