Somebody as dependent of I-485 application got a letter recently from USCIS like below:
Based on your request we researched the status of this case. We are actively processing this case. However, we have to perform additional review on this case and this has caused a longer processing time. If you do not receive a decision or other notice of action from us within 6 months of this letter, please call......
How, my question is what is the content of " addition review"
Many thanks!