Hi there! I understand you're encountering a white screen or an error message when trying to log into the UnitedHealthcare app. To help you better, can you tell me if this issue occurs right after you enter your username and password, or does it happen immediately when opening the app? Also, are you trying this on your Windows 10 device's browser or a specific app?

Meanwhile, here are some initial steps that can often resolve this kind of problem:

1. Clear your browser cache and cookies: Since you mentioned WebKit on Windows 10, if you’re using a web browser (like Safari on Windows or another WebKit-based browser), clearing the browsing history and cached files can fix display issues like a white screen.

2. Update your browser: If your browser is outdated, it might not display the site properly. Windows 10 supports several browsers—make sure yours is updated to the latest version.

3. Try a different browser: If clearing cache and updating don't help, test logging in through a different browser like Microsoft Edge or Google Chrome to see if the issue persists.

4. Disable browser extensions: Sometimes add-ons or extensions interfere with website functionality. Temporarily disable them to rule this out.

If you’re using the UnitedHealthcare app instead of the browser, the steps would be different:

- Force close the app completely.
- Clear the app cache (if available).
- Ensure the app is updated to the latest version in the Microsoft Store or the device’s app store.
- Restart your device and try again.

If you have already done some of these steps, please let me know which ones so we can try more advanced troubleshooting. Would you like me to guide you through any of these steps?