I think I found the reason. Mathematica I2C support uses wrong I2C bus for accessing to SenseHAT. It is behind /dev/i2c-1 but Mathematica tries to use /dev/i2c-0. I created symbolic link from i2c-1 to i2c-0 and that tricks Mathematica. I will write new discussion to summarize this finding.

I think the issue may be with I2C detection:

pi@raspberrypi:~ $ wolfram
Wolfram Language 11.3.0 Engine for Linux ARM (32-bit)
Copyright 1988-2018 Wolfram Research, Inc.

In[1]:= FindDevices[]                                                                                                                      

DeviceOpen::cameraDisconnected: The camera is not detected.  Please ensure the camera module is connected properly.

Out[1]= {DeviceObject[{FunctionDemo, 1}], DeviceObject[{GPIO, 1}], DeviceObject[{RandomSignalDemo, 1}], DeviceObject[{WriteDemo, 1}]}

In[2]:= FindDevices["I2C"]                                                                                                                 

Out[2]= {}

In[3]:=       

However python works for SenseHAT:

pi@raspberrypi:~ $ python
Python 2.7.13 (default, Nov 24 2017, 17:33:09) 
[GCC 6.3.0 20170516] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from sense_hat import SenseHat
>>> 
>>> sense = SenseHat()
>>> 
>>> sense.show_message("Hello world!")
>>> 

Hi Bradley,

My colleague Ian recently created a fix for this issue. To make sure you have the latest version of his MRAALink paclet, make sure your Pi is connected to the Internet, then run the following command in Mathematica:

PacletUpdate["MRAALink"]

This will update MRAALink to the latest version, which should solve your problem. Let me know if you have any other problems!