Some Cypress Flash devices provide the Vio option besides the Vcc core voltage. What if Vcc and Vio are coming from different supplies?
With this scenario, VCC (3.3V) was coming up before VIO (2.5V) with a time lag of up to 50ms. The concern was related to the Flash power-up initialization. This scenario, however, should be okay. Ensure that VIO is not higher than Vcc during power up. Lagging should not be an issue. RESET# must remain low until after VIO eventually comes up to desired level.