My problem was actually that I was using the wrong Chip Select line in hardware (connecting to a different pin on the processor). The pin that I connected to the CS line of the BMP280 was always low.What threw me off is that I was able to get the chip ID back from calling bmp280_init(dev), since that is the first SPI comminication that takes place. But because the CS line never went high again, all following communications to the chip were garbage. Something to think about when troubleshooting.
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