I fixed proximity sensor on p769 some time ago, I think p760 has the same hardware. The bug is random, that's why sometimes the sensor works, sometimes it don't.
Fix:
https://github.com/AntonX/lge-kernel-omap4/commit/8f4e9c63cb7d462a9ca930c6cf0eef6a92f29379
Fix:
https://github.com/AntonX/lge-kernel-omap4/commit/8f4e9c63cb7d462a9ca930c6cf0eef6a92f29379