What happens if you swap the lines
MAX6675 ktc(13, 7, 12); // Create a Module (CLK, CS, SO)
RF24 radio(9, 10); // Create a Radio (CE, CSN)
It may be that the RF24 library is setting SPI to a way that is incompatible with the MAXxxx
If so you will probably need to modify one of the libraries.
...R