If the Project is set as Tentative when archived, it will not appear in the reports section.
This is because Tentative projects are designed for future planning purposes.
For archived tentative projects with only past assignments, it is assumed that they did not happen and will not be tracked in the reports.
If you would like it to show up in the reports, you can set it as a confirmed project:
On the top menu bar, hover your cursor on Manage
On the right hand side, find Filter and choose Archived
Find the archived project that you would like to see on the reports
Click the 3-dot button and choose Edit Project
Set Project Status as Confirmed