I've not used a Teensy but I know they are fast micros. I would try sending just 1 byte and see what happens. With slower micros like an 328P based UNO, it's easy to overwhelm the receiving SPI device with bytes. Even with a teensy, you may have to put short delays in between each byte you send.
However, the Teensy my handle SPI differently and this may not be an issue. Hopefully a Teensy user will clarify this.