I don't usually deal with analytics, but the person on our team that does asked me this question, and I don't know the answer. She ran a report both in Community Analytics and in Admin User Reports for the exact same time period looking at the activity of one of our members (Rimser). I reproduce her reports. Here's what the reports show.
Admin User Reports:
Big difference in the number of replies. 100 vs 73. Why the big difference?
I believe this is due to Community Analytics being daily export to our BI, whereas the Admin metrics are real time. So that 24hr lag in CA should account for the difference as that user does appear to post frequently https://community.microfocus.com/t5/user/viewprofilepage/user-id/264852
I hope that is the case for this query.
Some caveats / pitfalls / known problems:
Generally it's best to stick with one metric source and not comparing across since there are important differences in how both metrics are captured. See Comparing Community Analytics and Admin metrics