I'm using project collaboration (https://collaboration.dataminer.services/) to verify the status of my project but I don't see the closed tasks. Where can I find the closed tasks?
Ben Vandenberghe [SLC] [DevOps Enabler] Selected answer as best 24th September 2020
This is working for me. Maybe it was related to the higher number of closed tasks that had to be fetched in your case? 
Ben Vandenberghe [SLC] [DevOps Enabler] Answered question 24th September 2020