Not to surrender to gremlins but I think there may be some signal integrity issue with the board. My board? It seems the flash is not erasing so I put my scope on the flash pins to do protocol decode. Everything seems to be ok protocol wise, but looking at the flash datasheet you may need a second command to reset the flash via SPI commands. Regardless, if I have the scope probes on the flash pins the erase command works. If I dont have them connected the erase command does not / is intermittent.