That display is an indication of a failure in the CAN High circuit. Probably the gauge cluster isn't able to communicate with the ECM or BCM on CAN H. You will need an oscilloscope to troubleshoot the CANBUS lines. Could be a wiring issue or more likely one of the modules is shorted or open on the CAN H and pulling the signal up/down or causing it to float due to a termination circuit failure.
https://support.squarell.com/index.php?/Knowledgebase/Article/View/94/0/can-high--can-low
Replacing the computer requires reprogramming the immobilizer - which is synced between the ECM, Body Module (BCM), the gauge cluster, and the chip key.
This is very involved level of diagnostics that many shops are not equipped for. Even many dealers have no one on staff that is capable of diagnosing this. You will need to find someone in your area that is familiar with CANBUS diagnostics AND the proclivities of Subaru's.
GD