That means: The officer of service center had doubt

for your application,so he/she couldn't make a final decision on your case,then transferred the case to local office,let the officer of local office to do it.
Sometimes,the local officer just ask a few questions,then approve your case,if he/she think it
isn't a big problem,but transfer to local will delay your case processing ,from a few months to 1-2 years.