In reply to Ben:
Hi Ben, I think your problem is related to the object compatibility when you do your $cast inside the register adapter. Probably you are not picking up the same object as you think, Can you show to us what is inside your user_reg_extension and how do you get it? Also looking into your write operation, there’s no object being passed like the example below.
reg_map.user_reg_xxh.write(status, data, UVM_FRONTDOOR, .parent(this), .extension(some_object));