SD cards have been known to Not release the MISO line. Try adding one gate of a buffer like 74HC125 on MISO coming back from the SD, with it's OE/ driven by CS going to the SD card.
SD cards have been known to Not release the MISO line. Try adding one gate of a buffer like 74HC125 on MISO coming back from the SD, with it's OE/ driven by CS going to the SD card.