SPI interface issue with MAX31856
I would slow things WAY down.  When debugging problems like this, put the clocks and signals in the KHz range so your tools give you good information.  You can speed things up later when you know they're working.
You are almost certainly violating tCWH (CS inactive time) of 400ns.
Don't bother with the write.  After power-on, just read a couple bytes starting from 0 until you can see the 0x03, 0xFF, 0x7F, 0xC0, 0x7F factory default sequence from the memory map.
Good luck.