Safari does not render Gmail correctly
I am the tech support for a university and this one has me stumped.
Only in Safari, when this specific user logins, it does not render Gmail correctly. Only Gmail. Only in Safari.
Using other Google Apps or using other browsers it works fine. If I login to Gmail, on Safari, while his account is logged in, it works fine.
OS-X 10.12.6
Things tried:
1. Clear cache/cookies
2. Disabling cache using Developer Mode in Safari
3. Updated operating system (he was on 10.12.2)
4. Switch to IE11 rendering engine in Safari, using Developer Mode
5. Confirmed it does work in other browsers.
6. Removed theme picture. It is now a blank white page, with the same error.
MacBook Air, macOS Sierra (10.12.6)