To fix the intermittent issue with typing Vietnamese in Gmail using VPSKEYS on Windows 10, you can try the following steps:
1. Make sure you have the latest version of VPSKEYS installed.
2. Restart your computer and try again.
3. Ensure that VPSKEYS is enabled and running in the background before starting Gmail.
4. Disable any conflicting keyboard or language input settings on your computer.
5. Clear your browser cache and cookies, then restart the browser.
6. If the problem persists, you may consider using alternative Vietnamese input methods or contacting VPSKEYS support for further assistance.