1. Billing hourly time
2. Completing a milestone
3. Bidding on a job
On the 3 factors you listed, No.2 would have gotten my last showing as just a day or so before as I'd submitted a milestone thereabouts. Maybe the delay in updating has something to do with the hitches that prevail currently.
Hi Mercy and others,
I got a confirmation from the team that "Last Active" is based on freelancers' activity on their open contracts (logging time or submitting milestones) or sending proposals for job postings.