There could be several reasons why the leave type is not loading for some customers in the Odoo mobile app. Here are a few things you could try to troubleshoot the issue:

1. Check the network connection: Make sure that the mobile device has a stable internet connection. If the device is connected to a weak or unstable network, it may be unable to load the leave type.

2. Check the app permissions: Make sure that the Odoo mobile app has the necessary permissions to access the internet and other resources. You can check and manage app permissions in the device's settings.

3. Check the app configuration: Make sure that the Odoo mobile app is correctly configured to connect to the correct server and database. You can check the app's configuration in the app settings.

4. Check the server logs: If the issue is related to the server, you may be able to find more information in the server logs. To access the server logs, you can go to "Settings > Technical > Logs > Server Actions".

5. Check for updates: Make sure that you are using the latest version of the Odoo mobile app. You can check for updates in the app store or play store.

I hope these suggestions are helpful. If you are still unable to resolve the issue, please provide more information about your setup and any error messages that you are seeing, and I will do my best to help troubleshoot the problem.