Hi Charles,
From your schematics it looks like the NAND is powered from 1.8V. Are the AM335X pins powered from 1.8V too? Check especially the GPMC_WAIT0 pin - it's on a different power domain and many people forget it. If it's powered from 3.3V you will need to connect the pullup R235 to 3.3V too.
Also the 470Ohm resistor is a bad idea I think. This can cause big voltage fluctuations when NAND consumption changes.