In reply to Peter Simon:
I was referring UVM 1.1d, so not sure if it can explain the difference, anyway, looks like it is not the root cause, sorry about that.
I was thinking if the root cause is that uvm_reg_block wasn’t registered into factory. I saw register your specific derived class : a_reg_block with utility `uvm_object_utils, but I was wondering about that if UVM_LIB registered uvm_reg_block into factory ? Probably it is the cause ?