It looks to me like subtasks and copying tasks might be the source of confusion.
Adding a project to a subtask will make that subtask show up as its own task in the project view instead of limiting its visibility to only within the parent task. If you then copy a parent task (I see “duplicated task from …” messages in the task history) the copied tasks and subtasks will have the projects assigned in the same way (the copy screen lets you change this behavior). This means you end up with a bunch of copies of the same task up at the project level and no easy way to tell them apart.
So in your screenshot, on the right-hand pane, the “Skrive blogposten - 3x3 - nevne vendors” is a subtask of the “Photo blog post” task which is the subtask of the “Wedding client workflow” parent task. In the left pane all the subtasks are the ones that have gray text to the right of the task name and this means all the subtasks must have been assigned the “Clients” project as well to show up there.
Typically I prefer to not add subtasks to projects just for this reason. If I do, I tend to go through and put info in the subtask’s name to differentiates it from other subtasks with the exact same name.
Here’s an example of mine:
I think I have a project that does something similar. I have a template project called “Templates” where I have a set of tasks with subtasks:
When I copy this task, I always rename it (hence the [insert view name] in the title). I also include instructions on how to handle the template tasks in each one so people know what to do when they get one of these.
There’s a lot of built in subtasks that have subtasks of their own. In this one the main task is two tasks deep (subtask of “create doc…” and “TEMPLATE: Create query…”):
I do tend to add these subtasks to a project, but only as I assign them to individuals and they become “workable” otherwise they clutter up the overall project and I only want to see work that needs to get done, not work that’s nowhere ready to show up. When I do assign these subtasks, I also add details to them that makes it so I can differentiate between them in the project view:
Hopefully this gives you some info on why you’re seeing so many tasks in your project and also how to manage them.