strange behavior in the spi_flash example

[msfassarella]

Hi guys,

I'm learning Zephyr and I'm using the code at sample/drivers/spi_flash.
I have the board RAK5010 that has a Nordic NRF52840 whit an external IS25WP064 qspi flash device.
Everything looks to work fine, but when I put a k_msleep(500) in some points of the code it returns strange results.
For example, if I put the k_msleep at beginning of the code, the first while loop returns zero in the buffer, but if comments this delay the first loop returns the right data.

`

 printk("\n" FLASH_NAME " SPI flash testing\n");
 printk("==========================\n");

k_msleep(500);    /*  generate an error on flash_read_jedec_id */
flash_dev = device_get_binding(FLASH_DEVICE);
if (!flash_dev) {
	printk("SPI flash driver %s was not found!\n", FLASH_DEVICE);
	return;
}
while (jed_buf[0] == 0) {
	cnt++;
	rc = flash_read_jedec_id(flash_dev, &jed_buf[0]);
	printk("ret: %d, loop #: %d, jedecid: %x %x %x\n", rc, cnt, jed_buf[0], jed_buf[1],
	       jed_buf[2]);
}

`

**Output without delay **

00> *** Booting Zephyr OS build v2.7.99-ncs1 ***
00>
00> JEDEC QSPI-NOR NORDIC SPI flash testing
00>
00> ==========================
00>
00> ret: 0, loop #: 1, jedecid: 9d 70 17
00>

**Output with delay **

00>
00> JEDEC QSPI-NOR NORDIC SPI flash testing
00>
00> ==========================
00>
00> ret: 0, loop #: 1, jedecid: 0 0 0 ======> Something is wrong here
00>
00> ret: 0, loop #: 2, jedecid: 9d 70 17

There are many other places where the k_msleep causes an unexpected behavior.
The complete code can be viewed here.
main.zip

I will appreciate very much if someone would explain why this happen.
Thanks.