Hello @Pablo_Ramos
Thank you for reaching out.
I've mistakenly changed the values of NON-VOLATILE configuration register. Now the flash is running in XIP mode instead of SPI mode. For deactivating XIP mode, flash device datasheet mentioned particular procedure which I'll provide below. How to send the bit on DQ0 on first clock dummy cycle? 
We have a lookup table in the flexspi_nor_polling_transfer SDK example. We include the FAST READ command in the sequence, but how do we transfer the XIP termination bit during the first dummy cycle?