Hi alican
The SimpleRX demo should not put the DW1000 in deepsleep. Not being able to read the devID could be due to multiple reasons, in your case it’s probable the SPI fast rate not working correctly.
A SPI speed of 3MHz should work in theory but will limit usability. Most UWB applications like TWR are time critical, you want to have fast communication between the MCU and DW1000 to ensure e.g the full frame can be sent to the chip before the TX timer times out or the receiver reception times out. See the notes in the TWR examples.
I would suggest using a MCU capable of higher SPI speeds unless you are only interested in transferring data at a limited data rate.