1. complete tasks in project
2. Delete project
3. go to view all completed
4. tasks from that projet appear, but without any project label.
Thank you for your report. That is currently the "correct" behavior because when a project is deleted, all information about it is removed incl. its name. So when a task (even completed) refers to the project's ID, this ID no longer exists in the system.
We'll look into improving this in the future and keep storing some project data after deletion.
This has now been fixed and you will see the project name next to tasks you complete and then delete their project.