Some tasks with 2 projects are not shown in one of them

Is there some trick that I don’t know? I assumed that when I add a task to two or more projects it will be visible in all of them. I have few of such tasks and I do see them in all projects they belong to. However, I have also some tasks that belong to more projects and they’re visible only on one of them.

What am I missing?

Hi
Have you checked the view settings for the projects where the task does not appear?
Maybe those projects only show incompleted or only completed tasks.

Thanks, haven’t thought about that.
It turned out that the main task is completed but the sub-task is not, hence the lack of it on the list.