when i try to write to sector3 and sector4 of NVM registers of STUSB4500 sector3 registers are all set to 1 why that was happening?

[Vkj.1]

when i try to write to NVM register sector4 alone it works fine but when i try to write to sector3 and sector4,by calling the two functions to write to sector3 and sector4 .sector3 registers are all set to 1