Hi, I have been facing the same problem with my sensors. I am using teensy 4.0 with teensyduino.
In my case, the sensors work fine separately but when I connect 2 or more sensors to the microcontroller, the initialisation fails.
@pylon The complete bus is (45+45+15+15+20) cm = 140 cm long. SPI connection limits are between 5-10 m so I don't think long bus wires should be a problem. But I am not sure.
This is the sensor that I am currently using
However, when I use pmw3901 form another manufacturer (https://www.tindie.com/products/onehorse/pmw3901-optical-flow-sensor/), the problem is solved. i.e this sensor which is smaller works fine separately and in a group of 4.
Please could someone suggest what might be causing the problematic sensors to behave in this way?