Thank you.
Could there be any reason causing the delay of my application since only FSW O is affected?
You are Federal Skilled Worker Inland. As of now it seems that both inland and outland FSWs are slow, (last FSW that got the Medical pass and/or Biometric Instruction Letter (BIL) had an AOR on the 22nd November).
So now, from what I see from the September, October and November threads, it seems that IRCC stopped giving MEP/BIL to FSWs for the past 2 days and moved on to giving final decisions to the Provincial Nominee Program (PNP) applications and the MEP/BIL to the December PNPs. I might be mistaken though as I am only basing my analysis on 2 days data and my own opinion.