Erase of internal flash is erasing intermediate some places only in one sector if caches are enabled in F767 controller.How caches effect flash sector erase

I am not able write anything once i write FF value into flash.Does writing FF into erased area blocks the region from writing again till that page is erased?

tcpip thread message fetch is not working in lwIP if caches enabled in STM32F767.How to align  lwIP driver Rx data buffers to cache line size.