So, I had a similar issue and did everything that the above mentioned. I went digging into the Apple Documentation and also to an Apple Store to speak to a Genius and this is what I found:
* When doing a replacement/swap of the top case and/or Touch ID sensor, it needs to be logged into AST 2 as being performed by an Apple Tech or Certified Apple Repair Facility
* The reason for the above is because the Touch ID needs to be “Serialized” to the new/existing motherboard (i.e. if you kept your motherboard but got a new top case or Touch ID, only a certified repair can initialize the secure enclave within the Touch ID sensor)
* The power button/function will still work, but the security of the Touch ID will not work until you serialize it
* The only way to “initialize/serialize” the Touch ID is by running a diagnostic/serialization via AST2
* AST 2 can only run the serialization if it has both the old and new serial numbers (i.e. if replacing the top case, you need the top case serial number of both top cases)
* Only certified techs can run the tool via the AST 2
So…that being said, if the process wasn’t done via AST 2 with a certified repair facility, chances are on T2 macs, the touch ID won’t work. This removes the function of “right to repair” as you cannot replace the sensor/button on your own without having to go to a certified facility to do the repair there.