Is 3 months time usual for RFE review by USCIS

HI Saurabh,

I have got my RFE response review on Sep4th and mostly the response by USCIS is sent within 2 months window. But for my case it has been almost 2.5 months and still the case is in RFE review status.
Can you please share your thoughts on what could be the reason for this delay and if this is usual case?