Need help to understand why microsoft is asking me to give 3 HM rounds

Recently interviewed at Microsoft. All 4 rounds went pretty well and in HM round the manager talked about teams which i can select to join. Today recruiter called and asked me to appear for two more HM rounds 30 min each. AFAIK microsoft takes only 4 rounds in most cases and if needed they go for additional technical rounds. Any info on why additional HM rounds are taken in my case.