The WP# can be connected to VDD or left open in the design. The WP is not driven by the flash so the flash is not setting it to low. Can you recheck again for any short-circuit or wrong connections on the pin. Is it possible for you to pull up the pin or tie it to VCC and then check its voltage level.
The pin should be internally pulled up to VDD if left floating. If you find no errors at your end then we need to check on the device.
Also can you let us know as to how many devices are showing this behavior.
Thanks and Regards,
I have three same board with the S29GL-S nor flash, all WP pin of the chip on three board is 0.4V. When I pull-up WP pin on the external, it is 3.3V, and high level. I have check WP pin ,and make sure that WP pin is not short to other pin, VCC and gound. I dont kown why ?