Check if the Quad Enable (QE) bit in the Configuration Register of the flash is set to 1. If the QE-Bit is set or not depends on the last access to the flash.
- This will be done automatically, when you configure Flash with Vivado or SDK and Flash in the design is specified as X4.
- This will be not always done automatically, when you use other software to get access. For example Xilinx barmetal lib doesn't check if the QE bit is set or not.